diff --git a/app/Audit/AbstractAuditLogFormatter.php b/app/Audit/AbstractAuditLogFormatter.php
index 6cad9869a..580c01dda 100644
--- a/app/Audit/AbstractAuditLogFormatter.php
+++ b/app/Audit/AbstractAuditLogFormatter.php
@@ -74,6 +74,70 @@ protected function processCollection(PersistentCollectionMetadata $metadata): ?a
         ];
     }
 
+    /**
+     * Shared handler for EVENT_COLLECTION_MANYTOMANY_UPDATE / DELETE (ADR-004).
+     *
+     * Runs the two-step pipeline (handleManyToManyCollection -> processCollection) and builds
+     * "<label> <field> (<TargetEntity>) updated: Added IDs: [..], Removed IDs: [..] by user X"
+     * or "<label> <field> (<TargetEntity>) deleted: Removed IDs: [..] by user X".
+     * Returns null when there is nothing to report, so the entry is not logged.
+     *
+     * A concrete formatter only has to route both event types here from its own
+     * EVENT_COLLECTION_MANYTOMANY_* case and provide the entity wording as $label.
+     */
+    protected function formatManyToManyCollectionChange(array $change_set, string $label): ?string
+    {
+        $metadata = $this->handleManyToManyCollection($change_set);
+        if ($metadata === null) {
+            return null;
+        }
+
+        $collectionData = $this->processCollection($metadata);
+        if (!$collectionData) {
+            return null;
+        }
+
+        $field = $collectionData['field'] ?? 'unknown';
+        $target = $collectionData['target_entity'] ?? 'unknown';
+        $added_ids = $collectionData['added_ids'] ?? [];
+        $removed_ids = $collectionData['removed_ids'] ?? [];
+
+        if ($this->event_type === Interfaces\IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE) {
+            if (empty($removed_ids)) {
+                return null;
+            }
+
+            return sprintf(
+                "%s %s (%s) deleted: Removed IDs: %s by user %s",
+                $label,
+                $field,
+                $target,
+                json_encode($removed_ids),
+                $this->getUserInfo()
+            );
+        }
+
+        $parts = [];
+        if (!empty($added_ids)) {
+            $parts[] = 'Added IDs: ' . json_encode($added_ids);
+        }
+        if (!empty($removed_ids)) {
+            $parts[] = 'Removed IDs: ' . json_encode($removed_ids);
+        }
+        if (empty($parts)) {
+            return null;
+        }
+
+        return sprintf(
+            "%s %s (%s) updated: %s by user %s",
+            $label,
+            $field,
+            $target,
+            implode(', ', $parts),
+            $this->getUserInfo()
+        );
+    }
+
 
     /**
      * Extract IDs from entity objects in collection
diff --git a/app/Audit/ConcreteFormatters/PresentationCategoryAuditLogFormatter.php b/app/Audit/ConcreteFormatters/PresentationCategoryAuditLogFormatter.php
index 46cf82dc5..762d66131 100644
--- a/app/Audit/ConcreteFormatters/PresentationCategoryAuditLogFormatter.php
+++ b/app/Audit/ConcreteFormatters/PresentationCategoryAuditLogFormatter.php
@@ -66,6 +66,10 @@ public function format($subject, array $change_set): ?string
                         $summit_name,
                         $this->getUserInfo()
                     );
+
+                case IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE:
+                case IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE:
+                    return $this->formatManyToManyCollectionChange($change_set, sprintf("Presentation Category '%s' (%s) (%s) for Summit '%s'", $title, $code, $id, $summit_name));
             }
         } catch (\Exception $ex) {
             Log::warning("PresentationCategoryAuditLogFormatter error: " . $ex->getMessage());
diff --git a/app/Audit/ConcreteFormatters/PresentationFormatters/PresentationSpeakerAuditLogFormatter.php b/app/Audit/ConcreteFormatters/PresentationFormatters/PresentationSpeakerAuditLogFormatter.php
index 09f85af47..2243985c1 100644
--- a/app/Audit/ConcreteFormatters/PresentationFormatters/PresentationSpeakerAuditLogFormatter.php
+++ b/app/Audit/ConcreteFormatters/PresentationFormatters/PresentationSpeakerAuditLogFormatter.php
@@ -62,6 +62,10 @@ public function format($subject, array $change_set): ?string
                         $email,
                         $this->getUserInfo()
                     );
+
+                case IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE:
+                case IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE:
+                    return $this->formatManyToManyCollectionChange($change_set, sprintf("Speaker '%s' (%s)", $full_name, $speaker_id));
             }
         } catch (\Exception $ex) {
             Log::warning("PresentationSpeakerAuditLogFormatter error: " . $ex->getMessage());
diff --git a/app/Audit/ConcreteFormatters/SelectionPlanAuditLogFormatter.php b/app/Audit/ConcreteFormatters/SelectionPlanAuditLogFormatter.php
index 75b9fe8c5..43ab5de73 100644
--- a/app/Audit/ConcreteFormatters/SelectionPlanAuditLogFormatter.php
+++ b/app/Audit/ConcreteFormatters/SelectionPlanAuditLogFormatter.php
@@ -80,6 +80,10 @@ public function format($subject, array $change_set): ?string
                         $summit_name,
                         $this->getUserInfo()
                     );
+
+                case IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE:
+                case IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE:
+                    return $this->formatManyToManyCollectionChange($change_set, sprintf("Selection Plan '%s' (%s) for Summit '%s'", $name, $id, $summit_name));
             }
         } catch (\Exception $ex) {
             Log::warning("SelectionPlanAuditLogFormatter error: " . $ex->getMessage());
diff --git a/app/Audit/ConcreteFormatters/SubmissionInvitationAuditLogFormatter.php b/app/Audit/ConcreteFormatters/SubmissionInvitationAuditLogFormatter.php
index 970b1daea..9762c381b 100644
--- a/app/Audit/ConcreteFormatters/SubmissionInvitationAuditLogFormatter.php
+++ b/app/Audit/ConcreteFormatters/SubmissionInvitationAuditLogFormatter.php
@@ -70,6 +70,10 @@ public function format($subject, array $change_set): ?string
                         $sent_status,
                         $this->getUserInfo()
                     );
+
+                case IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE:
+                case IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE:
+                    return $this->formatManyToManyCollectionChange($change_set, sprintf("Submission invitation for '%s' (%s)", $email, $id));
             }
         } catch (\Exception $ex) {
             Log::warning("SubmissionInvitationAuditLogFormatter error: " . $ex->getMessage());
diff --git a/app/Audit/ConcreteFormatters/SummitTrackChairAuditLogFormatter.php b/app/Audit/ConcreteFormatters/SummitTrackChairAuditLogFormatter.php
index a897275fc..32471cb59 100644
--- a/app/Audit/ConcreteFormatters/SummitTrackChairAuditLogFormatter.php
+++ b/app/Audit/ConcreteFormatters/SummitTrackChairAuditLogFormatter.php
@@ -63,6 +63,10 @@ public function format($subject, array $change_set): ?string
                         $member_id,
                         $this->getUserInfo()
                     );
+
+                case IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE:
+                case IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE:
+                    return $this->formatManyToManyCollectionChange($change_set, sprintf("Track Chair '%s' (%s)", $member_name, $member_id));
             }
         } catch (\Exception $ex) {
             Log::warning("SummitTrackChairAuditLogFormatter error: " . $ex->getMessage());
diff --git a/tests/OpenTelemetry/Formatters/PresentationCategoryManyToManyAuditLogFormatterTest.php b/tests/OpenTelemetry/Formatters/PresentationCategoryManyToManyAuditLogFormatterTest.php
new file mode 100644
index 000000000..e3bfdd529
--- /dev/null
+++ b/tests/OpenTelemetry/Formatters/PresentationCategoryManyToManyAuditLogFormatterTest.php
@@ -0,0 +1,156 @@
+<?php
+
+namespace Tests\OpenTelemetry\Formatters;
+
+/**
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+use App\Audit\ConcreteFormatters\PresentationCategoryAuditLogFormatter;
+use App\Audit\Interfaces\IAuditStrategy;
+use App\Models\Foundation\Summit\Events\Presentations\TrackQuestions\TrackQuestionTemplate;
+use Mockery;
+use models\main\Tag;
+use models\summit\PresentationCategory;
+use models\summit\Summit;
+use models\summit\SummitAccessLevelType;
+use Tests\OpenTelemetry\Formatters\Support\AuditContextBuilder;
+use Tests\OpenTelemetry\Formatters\Support\PersistentCollectionTestHelper;
+use Tests\TestCase;
+
+/**
+ * PresentationCategory owns three many-to-many collections: allowed_access_levels, allowed_tags and extra_questions.
+ */
+class PresentationCategoryManyToManyAuditLogFormatterTest extends TestCase
+{
+    private const MESSAGE_PREFIX = "Presentation Category 'AI' (AI01) (12) for Summit 'Test Summit'";
+
+    protected function tearDown(): void
+    {
+        Mockery::close();
+        parent::tearDown();
+    }
+
+    public function testUpdateEventReportsAddedAndRemovedIdsFromDiff(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('allowed_access_levels', SummitAccessLevelType::class, [10, 11], [11, 12]),
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " allowed_access_levels (SummitAccessLevelType) updated: Added IDs: [12], Removed IDs: [10] by user ",
+            $result
+        );
+    }
+
+    public function testUpdateEventReportsAddedIds(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('allowed_tags', Tag::class, [], [5, 6]),
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " allowed_tags (Tag) updated: Added IDs: [5,6] by user ",
+            $result
+        );
+    }
+
+    public function testDeleteEventReportsRemovedIdsFromPayload(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection'  => $this->makeCollection('allowed_access_levels', SummitAccessLevelType::class, [], []),
+            'deleted_ids' => [3, 4],
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " allowed_access_levels (SummitAccessLevelType) deleted: Removed IDs: [3,4] by user ",
+            $result
+        );
+    }
+
+    public function testUpdateEventWithoutDiffIsSuppressed(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('allowed_tags', Tag::class, [3], [3]),
+        ]);
+
+        $this->assertNull($result);
+    }
+
+    public function testDeleteEventWithNothingToRemoveIsSuppressed(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection'  => $this->makeCollection('allowed_tags', Tag::class, [], []),
+            'deleted_ids' => [],
+        ]);
+
+        $this->assertNull($result);
+    }
+
+    public function testManyToManyEventWithoutCollectionReturnsNull(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $this->assertNull($formatter->format($this->makeSubject(), []));
+    }
+
+    public function testManyToManyEventWithInvalidSubjectReturnsNull(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $this->assertNull($formatter->format(new \stdClass(), [
+            'collection' => $this->makeCollection('allowed_access_levels', SummitAccessLevelType::class, [], [7]),
+        ]));
+    }
+
+    private function makeFormatter(string $eventType): PresentationCategoryAuditLogFormatter
+    {
+        $formatter = new PresentationCategoryAuditLogFormatter($eventType);
+        $formatter->setContext(AuditContextBuilder::default()->build());
+        return $formatter;
+    }
+
+    private function makeCollection(string $field, string $targetEntity, array $snapshotIds, array $currentIds)
+    {
+        return PersistentCollectionTestHelper::buildManyToManyCollection(
+            PresentationCategory::class,
+            $field,
+            $targetEntity,
+            $snapshotIds,
+            $currentIds
+        );
+    }
+
+    private function makeSubject(): PresentationCategory
+    {
+        $summit = Mockery::mock(Summit::class);
+        $summit->shouldReceive('getName')->andReturn('Test Summit');
+
+        $category = Mockery::mock(PresentationCategory::class);
+        $category->shouldReceive('getId')->andReturn(12);
+        $category->shouldReceive('getTitle')->andReturn('AI');
+        $category->shouldReceive('getCode')->andReturn('AI01');
+        $category->shouldReceive('getSummit')->andReturn($summit);
+
+        return $category;
+    }
+}
diff --git a/tests/OpenTelemetry/Formatters/PresentationSpeakerManyToManyAuditLogFormatterTest.php b/tests/OpenTelemetry/Formatters/PresentationSpeakerManyToManyAuditLogFormatterTest.php
new file mode 100644
index 000000000..c02c13167
--- /dev/null
+++ b/tests/OpenTelemetry/Formatters/PresentationSpeakerManyToManyAuditLogFormatterTest.php
@@ -0,0 +1,152 @@
+<?php
+
+namespace Tests\OpenTelemetry\Formatters;
+
+/**
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+use App\Audit\ConcreteFormatters\PresentationFormatters\PresentationSpeakerAuditLogFormatter;
+use App\Audit\Interfaces\IAuditStrategy;
+use App\Models\Foundation\Main\Language;
+use Mockery;
+use models\summit\PresentationSpeaker;
+use models\summit\SpeakerActiveInvolvement;
+use models\summit\SpeakerOrganizationalRole;
+use Tests\OpenTelemetry\Formatters\Support\AuditContextBuilder;
+use Tests\OpenTelemetry\Formatters\Support\PersistentCollectionTestHelper;
+use Tests\TestCase;
+
+/**
+ * PresentationSpeaker owns three many-to-many collections: languages, organizational_roles and active_involvements.
+ */
+class PresentationSpeakerManyToManyAuditLogFormatterTest extends TestCase
+{
+    private const MESSAGE_PREFIX = "Speaker 'Jane Doe' (31)";
+
+    protected function tearDown(): void
+    {
+        Mockery::close();
+        parent::tearDown();
+    }
+
+    public function testUpdateEventReportsAddedAndRemovedIdsFromDiff(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('languages', Language::class, [10, 11], [11, 12]),
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " languages (Language) updated: Added IDs: [12], Removed IDs: [10] by user ",
+            $result
+        );
+    }
+
+    public function testUpdateEventReportsAddedIds(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('organizational_roles', SpeakerOrganizationalRole::class, [], [5, 6]),
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " organizational_roles (SpeakerOrganizationalRole) updated: Added IDs: [5,6] by user ",
+            $result
+        );
+    }
+
+    public function testDeleteEventReportsRemovedIdsFromPayload(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection'  => $this->makeCollection('languages', Language::class, [], []),
+            'deleted_ids' => [3, 4],
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " languages (Language) deleted: Removed IDs: [3,4] by user ",
+            $result
+        );
+    }
+
+    public function testUpdateEventWithoutDiffIsSuppressed(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('organizational_roles', SpeakerOrganizationalRole::class, [3], [3]),
+        ]);
+
+        $this->assertNull($result);
+    }
+
+    public function testDeleteEventWithNothingToRemoveIsSuppressed(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection'  => $this->makeCollection('organizational_roles', SpeakerOrganizationalRole::class, [], []),
+            'deleted_ids' => [],
+        ]);
+
+        $this->assertNull($result);
+    }
+
+    public function testManyToManyEventWithoutCollectionReturnsNull(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $this->assertNull($formatter->format($this->makeSubject(), []));
+    }
+
+    public function testManyToManyEventWithInvalidSubjectReturnsNull(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $this->assertNull($formatter->format(new \stdClass(), [
+            'collection' => $this->makeCollection('languages', Language::class, [], [7]),
+        ]));
+    }
+
+    private function makeFormatter(string $eventType): PresentationSpeakerAuditLogFormatter
+    {
+        $formatter = new PresentationSpeakerAuditLogFormatter($eventType);
+        $formatter->setContext(AuditContextBuilder::default()->build());
+        return $formatter;
+    }
+
+    private function makeCollection(string $field, string $targetEntity, array $snapshotIds, array $currentIds)
+    {
+        return PersistentCollectionTestHelper::buildManyToManyCollection(
+            PresentationSpeaker::class,
+            $field,
+            $targetEntity,
+            $snapshotIds,
+            $currentIds
+        );
+    }
+
+    private function makeSubject(): PresentationSpeaker
+    {
+        $speaker = Mockery::mock(PresentationSpeaker::class);
+        $speaker->shouldReceive('getId')->andReturn(31);
+        $speaker->shouldReceive('getFirstName')->andReturn('Jane');
+        $speaker->shouldReceive('getLastName')->andReturn('Doe');
+        $speaker->shouldReceive('getEmail')->andReturn('jane@example.com');
+
+        return $speaker;
+    }
+}
diff --git a/tests/OpenTelemetry/Formatters/SelectionPlanManyToManyAuditLogFormatterTest.php b/tests/OpenTelemetry/Formatters/SelectionPlanManyToManyAuditLogFormatterTest.php
new file mode 100644
index 000000000..86ef036fd
--- /dev/null
+++ b/tests/OpenTelemetry/Formatters/SelectionPlanManyToManyAuditLogFormatterTest.php
@@ -0,0 +1,148 @@
+<?php
+
+namespace Tests\OpenTelemetry\Formatters;
+
+/**
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+use App\Audit\ConcreteFormatters\SelectionPlanAuditLogFormatter;
+use App\Audit\Interfaces\IAuditStrategy;
+use App\Models\Foundation\Summit\SelectionPlan;
+use Mockery;
+use models\summit\PresentationCategoryGroup;
+use models\summit\Summit;
+use models\summit\SummitEventType;
+use Tests\OpenTelemetry\Formatters\Support\AuditContextBuilder;
+use Tests\OpenTelemetry\Formatters\Support\PersistentCollectionTestHelper;
+use Tests\TestCase;
+
+/**
+ * SelectionPlan owns two many-to-many collections: category_groups and event_types.
+ */
+class SelectionPlanManyToManyAuditLogFormatterTest extends TestCase
+{
+    private const PLAN_ID = 77;
+    private const PLAN_NAME = 'Main CFP';
+    private const SUMMIT_NAME = 'Test Summit';
+    private const MESSAGE_PREFIX = "Selection Plan 'Main CFP' (77) for Summit 'Test Summit'";
+
+    protected function tearDown(): void
+    {
+        Mockery::close();
+        parent::tearDown();
+    }
+
+    public function testCategoryGroupsUpdateEventReportsAddedAndRemovedIds(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makePlan(), [
+            'collection' => $this->makeCollection('category_groups', PresentationCategoryGroup::class, [10, 11], [11, 12]),
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " category_groups (PresentationCategoryGroup) updated: Added IDs: [12], Removed IDs: [10] by user ",
+            $result
+        );
+    }
+
+    public function testEventTypesUpdateEventReportsAddedIds(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makePlan(), [
+            'collection' => $this->makeCollection('event_types', SummitEventType::class, [], [5, 6]),
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " event_types (SummitEventType) updated: Added IDs: [5,6] by user ",
+            $result
+        );
+    }
+
+    public function testDeleteEventReportsRemovedIdsFromPayload(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE);
+
+        $result = $formatter->format($this->makePlan(), [
+            'collection'  => $this->makeCollection('category_groups', PresentationCategoryGroup::class, [], []),
+            'deleted_ids' => [3, 4],
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " category_groups (PresentationCategoryGroup) deleted: Removed IDs: [3,4] by user ",
+            $result
+        );
+    }
+
+    public function testUpdateEventWithoutDiffIsSuppressed(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makePlan(), [
+            'collection' => $this->makeCollection('event_types', SummitEventType::class, [3], [3]),
+        ]);
+
+        $this->assertNull($result);
+    }
+
+    public function testDeleteEventWithNothingToRemoveIsSuppressed(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE);
+
+        $result = $formatter->format($this->makePlan(), [
+            'collection'  => $this->makeCollection('event_types', SummitEventType::class, [], []),
+            'deleted_ids' => [],
+        ]);
+
+        $this->assertNull($result);
+    }
+
+    public function testManyToManyEventWithoutCollectionReturnsNull(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $this->assertNull($formatter->format($this->makePlan(), []));
+    }
+
+    private function makeFormatter(string $eventType): SelectionPlanAuditLogFormatter
+    {
+        $formatter = new SelectionPlanAuditLogFormatter($eventType);
+        $formatter->setContext(AuditContextBuilder::default()->build());
+        return $formatter;
+    }
+
+    private function makeCollection(string $field, string $targetEntity, array $snapshotIds, array $currentIds)
+    {
+        return PersistentCollectionTestHelper::buildManyToManyCollection(
+            SelectionPlan::class,
+            $field,
+            $targetEntity,
+            $snapshotIds,
+            $currentIds
+        );
+    }
+
+    private function makePlan(): SelectionPlan
+    {
+        $summit = Mockery::mock(Summit::class);
+        $summit->shouldReceive('getName')->andReturn(self::SUMMIT_NAME);
+
+        $plan = Mockery::mock(SelectionPlan::class);
+        $plan->shouldReceive('getId')->andReturn(self::PLAN_ID);
+        $plan->shouldReceive('getName')->andReturn(self::PLAN_NAME);
+        $plan->shouldReceive('getSummit')->andReturn($summit);
+
+        return $plan;
+    }
+}
diff --git a/tests/OpenTelemetry/Formatters/SubmissionInvitationManyToManyAuditLogFormatterTest.php b/tests/OpenTelemetry/Formatters/SubmissionInvitationManyToManyAuditLogFormatterTest.php
new file mode 100644
index 000000000..8dc3bb419
--- /dev/null
+++ b/tests/OpenTelemetry/Formatters/SubmissionInvitationManyToManyAuditLogFormatterTest.php
@@ -0,0 +1,152 @@
+<?php
+
+namespace Tests\OpenTelemetry\Formatters;
+
+/**
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+use App\Audit\ConcreteFormatters\SubmissionInvitationAuditLogFormatter;
+use App\Audit\Interfaces\IAuditStrategy;
+use Mockery;
+use models\main\Tag;
+use models\summit\SummitSubmissionInvitation;
+use Tests\OpenTelemetry\Formatters\Support\AuditContextBuilder;
+use Tests\OpenTelemetry\Formatters\Support\PersistentCollectionTestHelper;
+use Tests\TestCase;
+
+/**
+ * SummitSubmissionInvitation owns one many-to-many collection: tags.
+ */
+class SubmissionInvitationManyToManyAuditLogFormatterTest extends TestCase
+{
+    private const MESSAGE_PREFIX = "Submission invitation for 'ann@example.com' (9)";
+
+    protected function tearDown(): void
+    {
+        Mockery::close();
+        parent::tearDown();
+    }
+
+    public function testUpdateEventReportsAddedAndRemovedIdsFromDiff(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('tags', Tag::class, [10, 11], [11, 12]),
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " tags (Tag) updated: Added IDs: [12], Removed IDs: [10] by user ",
+            $result
+        );
+    }
+
+    public function testUpdateEventReportsAddedIds(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('tags', Tag::class, [], [5, 6]),
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " tags (Tag) updated: Added IDs: [5,6] by user ",
+            $result
+        );
+    }
+
+    public function testDeleteEventReportsRemovedIdsFromPayload(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection'  => $this->makeCollection('tags', Tag::class, [], []),
+            'deleted_ids' => [3, 4],
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " tags (Tag) deleted: Removed IDs: [3,4] by user ",
+            $result
+        );
+    }
+
+    public function testUpdateEventWithoutDiffIsSuppressed(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('tags', Tag::class, [3], [3]),
+        ]);
+
+        $this->assertNull($result);
+    }
+
+    public function testDeleteEventWithNothingToRemoveIsSuppressed(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection'  => $this->makeCollection('tags', Tag::class, [], []),
+            'deleted_ids' => [],
+        ]);
+
+        $this->assertNull($result);
+    }
+
+    public function testManyToManyEventWithoutCollectionReturnsNull(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $this->assertNull($formatter->format($this->makeSubject(), []));
+    }
+
+    public function testManyToManyEventWithInvalidSubjectReturnsNull(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $this->assertNull($formatter->format(new \stdClass(), [
+            'collection' => $this->makeCollection('tags', Tag::class, [], [7]),
+        ]));
+    }
+
+    private function makeFormatter(string $eventType): SubmissionInvitationAuditLogFormatter
+    {
+        $formatter = new SubmissionInvitationAuditLogFormatter($eventType);
+        $formatter->setContext(AuditContextBuilder::default()->build());
+        return $formatter;
+    }
+
+    private function makeCollection(string $field, string $targetEntity, array $snapshotIds, array $currentIds)
+    {
+        return PersistentCollectionTestHelper::buildManyToManyCollection(
+            SummitSubmissionInvitation::class,
+            $field,
+            $targetEntity,
+            $snapshotIds,
+            $currentIds
+        );
+    }
+
+    private function makeSubject(): SummitSubmissionInvitation
+    {
+        $invitation = Mockery::mock(SummitSubmissionInvitation::class);
+        $invitation->shouldReceive('getId')->andReturn(9);
+        $invitation->shouldReceive('getEmail')->andReturn('ann@example.com');
+        $invitation->shouldReceive('getFirstName')->andReturn('Ann');
+        $invitation->shouldReceive('getLastName')->andReturn('Lee');
+        $invitation->shouldReceive('isSent')->andReturn(false);
+        $invitation->shouldReceive('getSpeaker')->andReturn(null);
+
+        return $invitation;
+    }
+}
diff --git a/tests/OpenTelemetry/Formatters/SummitTrackChairManyToManyAuditLogFormatterTest.php b/tests/OpenTelemetry/Formatters/SummitTrackChairManyToManyAuditLogFormatterTest.php
new file mode 100644
index 000000000..13b8714a1
--- /dev/null
+++ b/tests/OpenTelemetry/Formatters/SummitTrackChairManyToManyAuditLogFormatterTest.php
@@ -0,0 +1,153 @@
+<?php
+
+namespace Tests\OpenTelemetry\Formatters;
+
+/**
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+use App\Audit\ConcreteFormatters\SummitTrackChairAuditLogFormatter;
+use App\Audit\Interfaces\IAuditStrategy;
+use Mockery;
+use models\main\Member;
+use models\summit\PresentationCategory;
+use models\summit\SummitTrackChair;
+use Tests\OpenTelemetry\Formatters\Support\AuditContextBuilder;
+use Tests\OpenTelemetry\Formatters\Support\PersistentCollectionTestHelper;
+use Tests\TestCase;
+
+/**
+ * SummitTrackChair owns one many-to-many collection: categories.
+ */
+class SummitTrackChairManyToManyAuditLogFormatterTest extends TestCase
+{
+    private const MESSAGE_PREFIX = "Track Chair 'Jane Doe' (5)";
+
+    protected function tearDown(): void
+    {
+        Mockery::close();
+        parent::tearDown();
+    }
+
+    public function testUpdateEventReportsAddedAndRemovedIdsFromDiff(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('categories', PresentationCategory::class, [10, 11], [11, 12]),
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " categories (PresentationCategory) updated: Added IDs: [12], Removed IDs: [10] by user ",
+            $result
+        );
+    }
+
+    public function testUpdateEventReportsAddedIds(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('categories', PresentationCategory::class, [], [5, 6]),
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " categories (PresentationCategory) updated: Added IDs: [5,6] by user ",
+            $result
+        );
+    }
+
+    public function testDeleteEventReportsRemovedIdsFromPayload(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection'  => $this->makeCollection('categories', PresentationCategory::class, [], []),
+            'deleted_ids' => [3, 4],
+        ]);
+
+        $this->assertStringStartsWith(
+            self::MESSAGE_PREFIX . " categories (PresentationCategory) deleted: Removed IDs: [3,4] by user ",
+            $result
+        );
+    }
+
+    public function testUpdateEventWithoutDiffIsSuppressed(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection' => $this->makeCollection('categories', PresentationCategory::class, [3], [3]),
+        ]);
+
+        $this->assertNull($result);
+    }
+
+    public function testDeleteEventWithNothingToRemoveIsSuppressed(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_DELETE);
+
+        $result = $formatter->format($this->makeSubject(), [
+            'collection'  => $this->makeCollection('categories', PresentationCategory::class, [], []),
+            'deleted_ids' => [],
+        ]);
+
+        $this->assertNull($result);
+    }
+
+    public function testManyToManyEventWithoutCollectionReturnsNull(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $this->assertNull($formatter->format($this->makeSubject(), []));
+    }
+
+    public function testManyToManyEventWithInvalidSubjectReturnsNull(): void
+    {
+        $formatter = $this->makeFormatter(IAuditStrategy::EVENT_COLLECTION_MANYTOMANY_UPDATE);
+
+        $this->assertNull($formatter->format(new \stdClass(), [
+            'collection' => $this->makeCollection('categories', PresentationCategory::class, [], [7]),
+        ]));
+    }
+
+    private function makeFormatter(string $eventType): SummitTrackChairAuditLogFormatter
+    {
+        $formatter = new SummitTrackChairAuditLogFormatter($eventType);
+        $formatter->setContext(AuditContextBuilder::default()->build());
+        return $formatter;
+    }
+
+    private function makeCollection(string $field, string $targetEntity, array $snapshotIds, array $currentIds)
+    {
+        return PersistentCollectionTestHelper::buildManyToManyCollection(
+            SummitTrackChair::class,
+            $field,
+            $targetEntity,
+            $snapshotIds,
+            $currentIds
+        );
+    }
+
+    private function makeSubject(): SummitTrackChair
+    {
+        $member = Mockery::mock(Member::class);
+        $member->shouldReceive('getId')->andReturn(5);
+        $member->shouldReceive('getFirstName')->andReturn('Jane');
+        $member->shouldReceive('getLastName')->andReturn('Doe');
+
+        $chair = Mockery::mock(SummitTrackChair::class);
+        $chair->shouldReceive('getMember')->andReturn($member);
+
+        return $chair;
+    }
+}