Security staff on the Eurostar are to go on strike next month.
Members of the RMT union will walk out on 16, 18, 22 and 23 December in a dispute over pay.
The strike will severely affect Eurostar services for travellers close to Christmas, the union said.
The workers, some of whom earn £10.66 an hour, rejected a below inflation pay offer and voted overwhelmingly for strike action.
More than 100 staff are expected to take part in the action.
Mick Lynch, general secretary of the union, said: “Eurostar security staff are essential to the running of Eurostar, and it is disgraceful they are not being paid a decent wage.”
He said they work “long, unsocial hours” and that a multimillion-pound company like Mitie “can easily afford to pay them decently”.
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“We do not want to disrupt people’s travel plans, but our members need a pay rise, and this is the only way management will listen,” he said.
He called on Mitie and Eurostar to come to a negotiated settlement with RMT as soon as possible.
The industrial action will coincide with other railway strikes – with RMT members at Network Rail and 14 train operators planning walkouts on 16 December.
Walkouts by train and railway station cleaners are due to take place on 22 and 23 December.