Eurostar is cutting 80 jobs, following a downturn in passenger numbers and ticket revenue, which the train company has partly attributed to the Brexit vote.
The company is also set to unveil a new international timetable in December, though it wouldn't confirm reports that it was cutting two daily trains to Paris and one to Brussels, after a decline in demand for travel.
Overall capacity is expected to stay the same as larger trains have been introduced, which can hold 900 people as opposed to 750 like the original fleet.
The operator of Channel Tunnel express services said it was in talks with unions about the job cuts across its business through voluntary redundancies and the offer of sabbatical leave.
The job losses will affect on-board staff, as well as office and depot workers, including in the capital.
A company spokeswoman said: "We're facing a challenging environment and are looking at the size and shape of our business."
The Transport Salaried Staffs' Association trade union said the cuts followed a "severe reduction in passenger numbers and revenue" this year, which had led to Eurostar "significantly reducing costs in other areas" before announcing the job losses.
In July, chief executive Nicolas Petrovic said Eurostar experienced "a slowdown in business travel and the uncertainty following the vote to leave, combined with the Brussels terrorist attack, has continued to dampen demand".
The company reported a three per cent drop in passenger numbers in the second quarter, compared with the same period last year. Revenue fell 10 per cent.
The train firm does still plan to bring in London-Amsterdam services next year.