More than 1,000 workers at ferry company P&O are to be balloted over industrial action against plans to cut 1,200 jobs.
The RMT union said the scale of the losses had angered workers in Dover, Hull and Portsmouth.
General secretary Bob Crow said: "Rather than sit down and discuss a long-term plan that would safeguard jobs, the company seems hell-bent on sacking hundreds, tearing up the contracts of those who are left, and even slashing payments to those prepared to leave the company voluntarily."
Ballot papers will be sent out next week, with a recommendation to vote for strikes, and the result will be known at the end of the month.
A P&O spokesman said the company was halfway into a three-month consultation process and was striving to resolve the issues.