diff --git a/apps/backend/src/application/auth/auth.service.ts b/apps/backend/src/application/auth/auth.service.ts
index 004951f..04d02e8 100644
--- a/apps/backend/src/application/auth/auth.service.ts
+++ b/apps/backend/src/application/auth/auth.service.ts
@@ -11,6 +11,7 @@ import * as argon2 from 'argon2';
 import { UserRepository, USER_REPOSITORY } from '@domain/ports/out/user.repository';
 import { User, UserRole } from '@domain/entities/user.entity';
 import { v4 as uuidv4 } from 'uuid';
+import { DEFAULT_ORG_ID } from '@infrastructure/persistence/typeorm/seeds/test-organizations.seed';
 
 export interface JwtPayload {
   sub: string; // user ID
@@ -221,8 +222,7 @@ export class AuthService {
 
     // Use default organization "Test Freight Forwarder Inc." if not provided
     // This ID comes from the seed migration 1730000000006-SeedOrganizations
-    const defaultOrgId = '1fa9a565-f3c8-4e11-9b30-120d1052cef0';
-    this.logger.log(`Using default organization ID for user registration: ${defaultOrgId}`);
-    return defaultOrgId;
+    this.logger.log(`Using default organization ID for user registration: ${DEFAULT_ORG_ID}`);
+    return DEFAULT_ORG_ID;
   }
 }
diff --git a/apps/backend/src/infrastructure/persistence/typeorm/migrations/1730000000007-SeedTestUsers.ts b/apps/backend/src/infrastructure/persistence/typeorm/migrations/1730000000007-SeedTestUsers.ts
index 8e7ec46..e387fae 100644
--- a/apps/backend/src/infrastructure/persistence/typeorm/migrations/1730000000007-SeedTestUsers.ts
+++ b/apps/backend/src/infrastructure/persistence/typeorm/migrations/1730000000007-SeedTestUsers.ts
@@ -2,36 +2,26 @@
  * Seed Test Users Migration
  *
  * Seeds test users for development and testing
- * Password for all users: AdminPassword123!
- * Hash generated with bcrypt rounds=10
+ * Password for all users: Password123!
+ * Hash generated with Argon2id
  */
 
 import { MigrationInterface, QueryRunner } from 'typeorm';
-import { v4 as uuidv4 } from 'uuid';
+import { DEFAULT_ORG_ID } from '../seeds/test-organizations.seed';
 
 export class SeedTestUsers1730000000007 implements MigrationInterface {
   public async up(queryRunner: QueryRunner): Promise<void> {
-    // Get the first organization ID from the database
-    const result = await queryRunner.query(`
-      SELECT id FROM organizations WHERE type = 'FREIGHT_FORWARDER' LIMIT 1
-    `);
+    // Use fixed organization ID from seed
+    const organizationId = DEFAULT_ORG_ID;
 
-    if (result.length === 0) {
-      throw new Error(
-        'No organization found to seed users. Please run organization seed migration first.'
-      );
-    }
+    // Pre-hashed password: Password123! (Argon2id)
+    // Generated with: argon2.hash('Password123!', { type: argon2.argon2id, memoryCost: 65536, timeCost: 3, parallelism: 4 })
+    const passwordHash = '$argon2id$v=19$m=65536,t=3,p=4$Uj+yeQiaqgBFqyTJ5FX3Cw$wpRCYORyFwjQFSuO3gpmzh10gx9wjYFOCvVZ8TVaP8Q';
 
-    const organizationId = result[0].id;
-
-    // Pre-hashed password: AdminPassword123! (bcrypt rounds=10)
-    // This hash is deterministic for testing purposes
-    const passwordHash = '$2b$10$5qK9KqP7YqXZ5Z0kZ0kZ0OqK9KqP7YqXZ5Z0kZ0kZ0OqK9KqP7YqX';
-
-    // Insert test users
+    // Fixed UUIDs for test users (matching existing data in database)
     const users = [
       {
-        id: uuidv4(),
+        id: 'c59ae389-da30-4533-be0c-fdfe6ac945de',
         email: 'admin@xpeditis.com',
         passwordHash,
         firstName: 'Admin',
@@ -39,7 +29,7 @@ export class SeedTestUsers1730000000007 implements MigrationInterface {
         role: 'ADMIN',
       },
       {
-        id: uuidv4(),
+        id: '496ba881-c055-4b78-b0c0-6c048215253b',
         email: 'manager@xpeditis.com',
         passwordHash,
         firstName: 'Manager',
@@ -47,7 +37,7 @@ export class SeedTestUsers1730000000007 implements MigrationInterface {
         role: 'MANAGER',
       },
       {
-        id: uuidv4(),
+        id: '361b409d-a32b-4ff9-a61b-e927450c1daf',
         email: 'user@xpeditis.com',
         passwordHash,
         firstName: 'Regular',
@@ -66,7 +56,10 @@ export class SeedTestUsers1730000000007 implements MigrationInterface {
           '${user.firstName}', '${user.lastName}', '${user.role}',
           '${organizationId}', NULL, true, NOW(), NOW()
         )
-        ON CONFLICT ("email") DO NOTHING;
+        ON CONFLICT ("email") DO UPDATE SET
+          "password_hash" = EXCLUDED."password_hash",
+          "organization_id" = EXCLUDED."organization_id",
+          "updated_at" = NOW();
       `);
     }
 
@@ -74,7 +67,7 @@ export class SeedTestUsers1730000000007 implements MigrationInterface {
     console.log('   - admin@xpeditis.com (ADMIN)');
     console.log('   - manager@xpeditis.com (MANAGER)');
     console.log('   - user@xpeditis.com (USER)');
-    console.log('   - Password: AdminPassword123!');
+    console.log('   - Password: Password123!');
   }
 
   public async down(queryRunner: QueryRunner): Promise<void> {
diff --git a/apps/backend/src/infrastructure/persistence/typeorm/seeds/test-organizations.seed.ts b/apps/backend/src/infrastructure/persistence/typeorm/seeds/test-organizations.seed.ts
index 8085d05..7eded0d 100644
--- a/apps/backend/src/infrastructure/persistence/typeorm/seeds/test-organizations.seed.ts
+++ b/apps/backend/src/infrastructure/persistence/typeorm/seeds/test-organizations.seed.ts
@@ -19,9 +19,14 @@ export interface OrganizationSeed {
   isActive: boolean;
 }
 
+// Fixed UUIDs for consistent seed data across environments
+export const DEFAULT_ORG_ID = 'c6042c7b-cffe-4fef-94f6-f27c2d0eb809';
+export const DEMO_CARRIER_ID = '462001d1-6829-4554-a4e1-477667edab6b';
+export const SAMPLE_SHIPPER_ID = '39e49605-5292-4935-9bff-c4abb547d3b9';
+
 export const organizationSeeds: OrganizationSeed[] = [
   {
-    id: uuidv4(),
+    id: DEFAULT_ORG_ID,
     name: 'Test Freight Forwarder Inc.',
     type: 'FREIGHT_FORWARDER',
     scac: null,
@@ -33,7 +38,7 @@ export const organizationSeeds: OrganizationSeed[] = [
     isActive: true,
   },
   {
-    id: uuidv4(),
+    id: DEMO_CARRIER_ID,
     name: 'Demo Shipping Company',
     type: 'CARRIER',
     scac: 'DEMO',
@@ -45,7 +50,7 @@ export const organizationSeeds: OrganizationSeed[] = [
     isActive: true,
   },
   {
-    id: uuidv4(),
+    id: SAMPLE_SHIPPER_ID,
     name: 'Sample Shipper Ltd.',
     type: 'SHIPPER',
     scac: null,