A protest has been held outside the Department for Transport office to call for guarantees that new ferry services aimed at easing pressure on Dover after Brexit will be crewed by UK seafarers.
Contracts worth more than £100 million have been awarded to three firms to lay on additional crossings, including Seaborne Freight, even though the company has never run a Channel service.
The Rail, Maritime and Transport union (RMT) demonstrated in London on Friday, calling for the ferries to comply with UK employment law and to be fully crewed with UK staff.
MT general secretary Mick Cash said: "These are UK Government ferry contracts and the Government would be quite within their rights to insist they are protected by UK employment law and crewed with UK seafarers.
"There has been a barrage of publicity around the Government's Brexit ferry contracts and the union has written to both Transport Secretary Chris Grayling, who is in control of the arrangements, and the companies involved demanding basic assurances on UK ratings jobs, union recognition and full compliance with UK employment laws.
"RMT has no intention of allowing any backsliding, or any stitch-ups of UK seafarers, and that is why we are making our position public with the protest at the Department for Transport.
"We expect Chris Grayling and the companies he has contracted to meet our demands in full as a matter of urgency."
Seaborne's deal to run freight services from Ramsgate has been questioned as the company has never run a ferry service and does not own any ships.