The results are due today of a ballot of workers at Irish Ferries on whether to strike following the company's decision to use "low-cost crews" on routes to France.
The unions confirmed last week that any strike action would not be limited by region and would take effect across all the company's services.
Irish Ferries said it was delighted with the response to the voluntary severance package on offer to the 150 crew, and that the ending of its direct staffing on the routes would result in no forced redundancies.
Workers who do not wish to leave the company will be moved to the Irish Sea services.
The company has seen a 7 per cent decrease in the volume of passengers on its services to France on last year and said such figures could not be sustained in the long term.