P&O ferries has announced it is to cut 1,200 jobs and close all but one of its Western Channel routes.
Workers at Dover, Portsmouth and Calais are expected to take the brunt of the job cuts with Union officials not ruling out industrial action.
The number of ships P&O operates will be cut from 31 to 23, and it will be closing all its Western Channel routes Routes from Portsmouth to Cherbourg, Le Havre and Caen.
The route from Rosslare to Cherbourg will also be stopped leaving just the Portsmouth-Bilbao service.
P&O said its tourist traffic had been "adversely affected by fewer day trips and the expansion of the low-cost airlines".
However, Brittany Ferries has signed an initial agreement with P&O to charter the two cruise ferries – Pride of Le Havre and Pride of Portsmouth.
Additionally, Brittany Ferries may re-align capacity on some of its existing routes.
New timetables covering any re-alignment and the provisional plans for the Portsmouth - Le Havre route will be announced in due course.