Eurostar staff rosters have been branded "unfair" by union bosses sparking warnings that staff may strike in the run-up to Christmas.
Members of both the RMT and TSSA trade unions have voted in favour of industrial action, which they hope will force Eurostar to rethink employee working patterns.
Gerry Doherty, TSSA general secretary, said that Eurostar was not dividing up the work fairly between French and British workers. "All our members want is for weekend duties to be shared equally among train managers on both sides of the channel," he said.
"Nobody wants to see services disrupted as Christmas approaches, but our members are telling us that they cannot accept unfair and imposed rosters that undermine their work-life balance."
RMT general secretary Bob Crow said: "Our members have told the company very clearly that imposing unfair and unequal rosters is no way to reward staff who did all they could to help Eurostar get back to normal after the recent Channel Tunnel fire.
"We hope the company will now get back in step with its own policy, withdraw these imposed rosters and get back around the table with us to find a fair and equitable solution."
RMT members voted 60 to four in favour of striking while TSSA members voted 11 to four. If an agreement is not negotiated, a strike could be held any time in the three weeks to Christmas.
It said the rosters and shift patterns were introduced after services were disrupted by the fire in September, and that they fully met the conditions of contract for all Eurostar UK train managers.
"We are extremely disappointed that our UK train managers have decided on this course of action and at this time, and we will make every effort to ensure our travellers face no further disruption in the busy period up to Christmas and the New Year," said customer services director Marc Noaro.