Cross-Channel rail operator Eurostar faces the threat of a strike over the busy Easter weekend.
About 100 staff based at St Pancras are being balloted for industrial action over the alleged victimisation of a union representative.
The Rail, Maritime and Transport union says that if its members vote in favour, the strike will go ahead from March 25.
The union claims an RMT representative and train manager is being victimised for objecting to managing a train along a section of the Eurostar route on her own.
The union insists that working alone is unsafe and the manager is within her rights to refuse.
Eurostar said it is in discussion with the union and hopes to find a solutuion.
