The rail company is facing the action after a train manager, who is also an RMT activist and union representative, was charged with gross misconduct.

She is being charged after objecting to an instruction to crew a Eurostar train which would have required her to work a section of the route alone. The union has concerns over staff working alone.

Now, they are urging nearly 100 train managers at St Pancras to vote for a strike before the poll closes on March 15, with the earliest date workers could then strike being March 22, three days before Good Friday.

RMT General Secretary Mick Cash said: “The outrageous decision taken by Eurostar management to discipline our member in this manner is totally unacceptable. This is a situation that the union will not allow to go unchallenged.

“Our members recognise full well that it could be them next and that it is imperative that they stand together.

“RMT is urging all members to demonstrate the strength of feeling to the company in this dispute by returning a massive yes vote in the ballot for industrial action.

“The risks of asking a member of staff to work alone are obvious to everyone and the fact that there is currently a heightened level of security alert on these international services only reinforces the union’s case.

“The union remains available for talks.”

A Eurostar spokesperson said the company does not comment on individual cases but added: “We are in ongoing discussions with the RMT to find a solution.”