diff --git a/apps/edr-passenger-api/src/modules/bookings/bookings.service.ts b/apps/edr-passenger-api/src/modules/bookings/bookings.service.ts
index 7f0a6eee5..6330c8cc6 100644
--- a/apps/edr-passenger-api/src/modules/bookings/bookings.service.ts
+++ b/apps/edr-passenger-api/src/modules/bookings/bookings.service.ts
@@ -13,6 +13,7 @@ import { FareEngineService } from '../fare-engine/fare-engine.service';
 import { PaymentsService } from '../payments/payments.service';
 import { MAX_PAYMENT_HOURS } from '../../common/utils/payment-deadline.utils';
 import { Currency, PassengerCategory, IdDocumentType } from '@prisma/client';
+import { JourneyDirection } from '../seats/seats.dto';
 import { resolveCurrencyFromNationality } from '../fare-engine/fare-engine.dto';
 import { DeleteOperationException } from '../../common/exceptions/delete-operation.exception';
 import { AuditService } from '../../common/audit.service';
@@ -856,6 +857,14 @@ export class BookingsService {
     const destStop = schedule.stopTimes.find(s => s.stationId === dto.destinationStationId);
     if (!originStop || !destStop) throw new NotFoundException('Origin or destination not found');
 
+    await this.seatsService.assertNoRouteSeatConflict({
+      scheduleId: dto.scheduleId,
+      seatIds: requestedSeatIds,
+      originStationId: dto.originStationId,
+      destinationStationId: dto.destinationStationId,
+      journeyDirection: JourneyDirection.ONE_WAY,
+    });
+
     const [passengersData, iamContact] = await Promise.all([
       this.processPassengers(dto.passengers as any[]),
       this.resolveIamContact(dto.passengerId),
@@ -1052,6 +1061,21 @@ export class BookingsService {
       throw new NotFoundException('Origin or destination stops not found');
     }
 
+    await this.seatsService.assertNoRouteSeatConflict({
+      scheduleId: dto.scheduleId,
+      seatIds: holdObSeatIds,
+      originStationId: dto.originStationId,
+      destinationStationId: dto.destinationStationId,
+      journeyDirection: JourneyDirection.OUTBOUND,
+    });
+    await this.seatsService.assertNoRouteSeatConflict({
+      scheduleId: dto.returnScheduleId,
+      seatIds: holdRetSeatIds,
+      originStationId: dto.returnOriginStationId,
+      destinationStationId: dto.returnDestinationStationId,
+      journeyDirection: JourneyDirection.RETURN,
+    });
+
     const [passengersData, iamContact] = await Promise.all([
       this.processRoundTripPassengers(dto.passengers as any[]),
       this.resolveIamContact(dto.passengerId),
@@ -1295,6 +1319,21 @@ export class BookingsService {
     if (!leg1OriginStop || !leg1DestStop) throw new NotFoundException('Leg-1 origin or transit station not found on schedule');
     if (!leg2OriginStop || !leg2DestStop) throw new NotFoundException('Transit or leg-2 destination station not found on leg-2 schedule');
 
+    await this.seatsService.assertNoRouteSeatConflict({
+      scheduleId: dto.scheduleId,
+      seatIds: leg1SeatIds,
+      originStationId: dto.originStationId,
+      destinationStationId: dto.transitStationId,
+      journeyDirection: JourneyDirection.ONE_WAY,
+    });
+    await this.seatsService.assertNoRouteSeatConflict({
+      scheduleId: dto.leg2ScheduleId,
+      seatIds: leg2SeatIds,
+      originStationId: dto.transitStationId,
+      destinationStationId: dto.leg2DestinationStationId,
+      journeyDirection: JourneyDirection.ONE_WAY,
+    });
+
     const [passengersData, iamContact] = await Promise.all([
       this.processPassengers(dto.passengers as any[]),
       this.resolveIamContact(dto.passengerId),
@@ -1490,6 +1529,35 @@ export class BookingsService {
     if (!retL1Origin || !retL1Dest) throw new NotFoundException('Return leg-1: origin or transit station not found');
     if (!retL2Origin || !retL2Dest) throw new NotFoundException('Return leg-2: transit or destination not found');
 
+    await this.seatsService.assertNoRouteSeatConflict({
+      scheduleId: dto.scheduleId,
+      seatIds: (dto.passengers as any[]).map(p => p.seatId),
+      originStationId: dto.originStationId,
+      destinationStationId: dto.transitStationId,
+      journeyDirection: JourneyDirection.OUTBOUND,
+    });
+    await this.seatsService.assertNoRouteSeatConflict({
+      scheduleId: dto.leg2ScheduleId,
+      seatIds: (dto.passengers as any[]).map(p => p.leg2SeatId ?? p.seatId),
+      originStationId: dto.transitStationId,
+      destinationStationId: dto.leg2DestinationStationId,
+      journeyDirection: JourneyDirection.OUTBOUND,
+    });
+    await this.seatsService.assertNoRouteSeatConflict({
+      scheduleId: dto.returnScheduleId,
+      seatIds: (dto.passengers as any[]).map(p => p.returnSeatId),
+      originStationId: dto.returnOriginStationId,
+      destinationStationId: dto.returnTransitStationId,
+      journeyDirection: JourneyDirection.RETURN,
+    });
+    await this.seatsService.assertNoRouteSeatConflict({
+      scheduleId: dto.returnLeg2ScheduleId,
+      seatIds: (dto.passengers as any[]).map(p => p.returnLeg2SeatId ?? p.returnSeatId),
+      originStationId: dto.returnTransitStationId,
+      destinationStationId: dto.returnLeg2DestinationStationId,
+      journeyDirection: JourneyDirection.RETURN,
+    });
+
     const [passengersData, iamContact] = await Promise.all([
       this.processRoundTripPassengers(dto.passengers as any[]),
       this.resolveIamContact(dto.passengerId),
diff --git a/apps/edr-passenger-api/src/modules/bookings/guest-booking.service.ts b/apps/edr-passenger-api/src/modules/bookings/guest-booking.service.ts
index c8061184f..4b3a9a53d 100644
--- a/apps/edr-passenger-api/src/modules/bookings/guest-booking.service.ts
+++ b/apps/edr-passenger-api/src/modules/bookings/guest-booking.service.ts
@@ -13,6 +13,7 @@ import { PaymentsService } from '../payments/payments.service';
 import { SmsClientService } from '../notifications/sms-client.service';
 import { CreateGuestBookingDto, SavedPassengerProfileDto, IssueReservationBookingDto, ReservationBookingKind } from './guest-booking.dto';
 import { Currency, PassengerCategory, IdDocumentType, PaymentMethodType, PaymentIntentStatus } from '@prisma/client';
+import { JourneyDirection } from '../seats/seats.dto';
 import { resolveCheckinCutoff } from '../../common/utils/checkin-cutoff.utils';
 import { computePaymentDeadline } from '../../common/utils/payment-deadline.utils';
 import { randomUUID } from 'crypto';
diff --git a/apps/edr-passenger-api/src/modules/seats/seats.service.spec.ts b/apps/edr-passenger-api/src/modules/seats/seats.service.spec.ts
index 2c4215dc8..e80966d6a 100644
--- a/apps/edr-passenger-api/src/modules/seats/seats.service.spec.ts
+++ b/apps/edr-passenger-api/src/modules/seats/seats.service.spec.ts
@@ -2,16 +2,47 @@ import { Test, TestingModule } from '@nestjs/testing';
 import { SeatsService } from './seats.service';
 import { PrismaService } from '../../common/prisma.service';
 import { ConflictException } from '@nestjs/common';
+import { SegmentsService } from '../segments/segments.service';
+import { SystemConfigService } from '../system-config/system-config.service';
+import { AuditService } from '../../common/audit.service';
+import { SmsClientService } from '../notifications/sms-client.service';
+import { JourneyDirection } from './seats.dto';
 
 describe('SeatsService - Auto Assign', () => {
   let service: SeatsService;
   let prisma: PrismaService;
+  let segmentsService: SegmentsService;
 
   const mockPrisma = {
     seat: {
       findMany: jest.fn(),
       updateMany: jest.fn(),
     },
+    tripStopTime: {
+      findMany: jest.fn(),
+    },
+    trainSchedule: {
+      findUnique: jest.fn(),
+    },
+    seatBlock: {
+      findMany: jest.fn(),
+    },
+  };
+
+  const mockSegmentsService = {
+    getSeatAvailabilityMap: jest.fn(),
+  };
+
+  const mockSystemConfigService = {
+    getNumber: jest.fn().mockResolvedValue(30),
+  };
+
+  const mockAuditService = {
+    log: jest.fn(),
+  };
+
+  const mockSmsClientService = {
+    send: jest.fn(),
   };
 
   beforeEach(async () => {
@@ -19,12 +50,67 @@ describe('SeatsService - Auto Assign', () => {
       providers: [
         SeatsService,
         { provide: PrismaService, useValue: mockPrisma },
+        { provide: SegmentsService, useValue: mockSegmentsService },
+        { provide: SystemConfigService, useValue: mockSystemConfigService },
+        { provide: AuditService, useValue: mockAuditService },
+        { provide: SmsClientService, useValue: mockSmsClientService },
       ],
     }).compile();
 
     service = module.get<SeatsService>(SeatsService);
     prisma = module.get<PrismaService>(PrismaService);
+    segmentsService = module.get<SegmentsService>(SegmentsService);
     jest.clearAllMocks();
+
+    mockPrisma.trainSchedule.findUnique.mockResolvedValue({
+      originStationId: 'origin-station',
+      destinationStationId: 'destination-station',
+    });
+    mockPrisma.tripStopTime.findMany.mockResolvedValue([
+      { stationId: 'origin-station', sequence: 0 },
+      { stationId: 'destination-station', sequence: 1 },
+    ]);
+    mockPrisma.seatBlock.findMany.mockResolvedValue([]);
+    mockSegmentsService.getSeatAvailabilityMap.mockResolvedValue(new Map());
+  });
+
+  describe('assertNoRouteSeatConflict', () => {
+    it('rejects overlapping origin-destination seat reuse on the same schedule', async () => {
+      mockPrisma.tripStopTime.findMany.mockResolvedValue([
+        { stationId: 'seb', sequence: 1 },
+        { stationId: 'ada', sequence: 2 },
+        { stationId: 'dd', sequence: 3 },
+      ]);
+      mockSegmentsService.getSeatAvailabilityMap.mockResolvedValue(new Map([['seat-1', 'BOOKED']]));
+      mockPrisma.seat.findMany.mockResolvedValue([
+        { id: 'seat-1', seatNumber: '12', coach: { number: 'C1' } },
+      ]);
+
+      await expect(service.assertNoRouteSeatConflict({
+        scheduleId: 'sched-1',
+        seatIds: ['seat-1'],
+        originStationId: 'seb',
+        destinationStationId: 'dd',
+        journeyDirection: JourneyDirection.ONE_WAY,
+      })).rejects.toThrow(ConflictException);
+    });
+
+    it('allows the same seat number to be reused on non-overlapping legs', async () => {
+      mockPrisma.tripStopTime.findMany.mockResolvedValue([
+        { stationId: 'seb', sequence: 1 },
+        { stationId: 'ada', sequence: 2 },
+        { stationId: 'dd', sequence: 3 },
+      ]);
+      mockSegmentsService.getSeatAvailabilityMap.mockResolvedValue(new Map());
+
+      await expect(service.assertNoRouteSeatConflict({
+        scheduleId: 'sched-1',
+        seatIds: ['seat-1'],
+        originStationId: 'seb',
+        destinationStationId: 'ada',
+        journeyDirection: JourneyDirection.ONE_WAY,
+      })).resolves.toBeUndefined();
+    });
   });
 
   describe('autoAssignSeats', () => {
diff --git a/apps/edr-passenger-api/src/modules/seats/seats.service.ts b/apps/edr-passenger-api/src/modules/seats/seats.service.ts
index 383f7d96c..83dc6aea4 100644
--- a/apps/edr-passenger-api/src/modules/seats/seats.service.ts
+++ b/apps/edr-passenger-api/src/modules/seats/seats.service.ts
@@ -209,6 +209,57 @@ export class SeatsService {
   // (availabilityByClass) use — so the seatmap and search results can never disagree
   // about seat availability again. Previously this method carried its own
   // separately-written copy of the same hold/JourneySegment-overlap logic.
+  async assertNoRouteSeatConflict(args: {
+    scheduleId: string;
+    seatIds: string[];
+    originStationId?: string;
+    destinationStationId?: string;
+    journeyDirection?: JourneyDirection;
+  }): Promise<void> {
+    const { scheduleId, seatIds, originStationId, destinationStationId, journeyDirection = JourneyDirection.ONE_WAY } = args;
+    if (!seatIds.length) return;
+
+    const stopTimes = await this.prisma.tripStopTime.findMany({
+      where: { scheduleId },
+      select: { stationId: true, sequence: true },
+    });
+
+    let reqFrom = -Infinity;
+    let reqTo = Infinity;
+    if (originStationId && destinationStationId) {
+      const seqOf = (stationId: string) => stopTimes.find(s => s.stationId === stationId)?.sequence;
+      const resolvedFrom = seqOf(originStationId);
+      const resolvedTo = seqOf(destinationStationId);
+      if (resolvedFrom !== undefined && resolvedTo !== undefined) {
+        reqFrom = resolvedFrom;
+        reqTo = resolvedTo;
+      }
+    }
+
+    const availability = await this.segmentsService.getSeatAvailabilityMap(
+      scheduleId,
+      seatIds,
+      stopTimes,
+      reqFrom,
+      reqTo,
+      journeyDirection,
+    );
+
+    if (availability.size === 0) return;
+
+    const seats = await this.prisma.seat.findMany({
+      where: { id: { in: seatIds } },
+      select: { id: true, seatNumber: true },
+    });
+    const byId = new Map(seats.map(seat => [seat.id, seat.seatNumber]));
+    const conflicts = seatIds.filter(id => availability.has(id));
+
+    if (conflicts.length > 0) {
+      const labels = conflicts.map(id => byId.get(id) ?? id).join(', ');
+      throw new ConflictException(`Seat(s) ${labels} are already assigned for this route on this schedule`);
+    }
+  }
+
   async resolveEffectiveStatuses(
     scheduleId: string,
     seatIds: string[],
@@ -424,6 +475,14 @@ export class SeatsService {
         throw new BadRequestException('Origin must come before destination');
 
       const currentDirection = dto.journeyDirection || JourneyDirection.ONE_WAY;
+      await this.assertNoRouteSeatConflict({
+        scheduleId: dto.scheduleId,
+        seatIds,
+        originStationId: dto.originStationId,
+        destinationStationId: dto.destinationStationId,
+        journeyDirection: currentDirection,
+      });
+
       const activeHolds = await tx.seatHold.findMany({
         where: { scheduleId: dto.scheduleId, expiresAt: { gt: new Date() } },
         select: { seatIds: true, createdBy: true },