Eurostar rail workers will launch a four-day strike today in a dispute over work/life balance.
Members of the Rail, Maritime and Transport (RMT) union will walk out until Monday, followed by three days over the Bank Holiday weekend from August 27.
A picket line will be mounted outside London's St Pancras railway station, where the trains leave for Paris and Brussels.
One train in each direction between London and Brussels has been cancelled today, but Eurostar said it expects to operate a normal service tomorrow.
The company said it was working on plans for Sunday and Monday and will be able to accommodate all customers booked to travel.
The union said the dispute centres on Eurostar's failure to honour an agreement from 2008 which sought to ensure that train managers could expect a good work/life balance in terms of unsocial hours and duty rosters.
RMT members voted in favour of strike action, claiming that their work/life balance was being "repeatedly undermined".
General secretary Mick Cash said: "Our train manager members at Eurostar have a heavy commitment to shift work and unsocial hours and are sick and tired of the company's failure to honour agreements.
"Our members have every right to have a fair work/life balance that fulfils the operational needs of the company while guaranteeing quality time off for friends and family.
"It's now time for Eurostar to come to the negotiating table with a set of proposals that honours our agreements and guarantees our members a genuine work/life balance."
Around 80 train managers are involved in the dispute.
A Eurostar spokesman said: "We are aware of the plans for strike action and our focus has been seeking a joint resolution whilst planning to provide a good service for our customers.
"On the days of the strike we have made some small changes to our timetable to ensure that all passengers booked to travel will be able to on those days. Passengers affected will be notified in advance."
The TSSA rail union announced that its train manager members on Eurostar will strike on August 14 and 15 and for two days over the Bank Holiday weekend - Sunday August 28 and Monday August 29 - in the same dispute.
General secretary Manuel Cortes said there was still a "window of opportunity" to solve the dispute in talks with management on Friday.
"This is a long-standing issue and there is still time to resolve it if common sense prevails on Friday," he said. "No-one wants to see disruption at holiday times and we will be working for a peaceful solution."