Talks are continuing between unions and management over planned strikes by security guards at the London and Ashford Eurostar terminals.
Action over pay by workers at Chubb is planned for this Friday and Saturday. Eurostar said it did not expect the strike to affect Bank Holiday weekend services.
The RMT union told BBC Radio Kent on Monday it was concerned at the train operator's view that a lack of security guards would have little effect.
Mick Cash, RMT assistant general secretary, said: "Our members are specially trained security guards doing work such as looking after x-ray machines, personal searches, metal detectors. For the company to say it will have little effect I find surprising and worrying."
The union is seeking an interim pay award while talks continue about a long-term pay deal. According to the union, an imposed rise of 3% was imposed this year but Cash said: "Three per cent of £6.36 an hour is not very high."