Train services across Wales will be halted today because of a strike by drivers in a row over pay and conditions.
Members of Aslef at Arriva Trains Wales will walk out for 24 hours, causing travel chaos on the first day back to work after the festive break.
The company said all its services were expected to be cancelled because of the strike ans some early morning trains on January 5 could also be disrupted.
A company statement said: "We deeply regret this disruption and continue to do all we can to avert strike action, however we are advising customers to make alternative travel arrangements for Monday January 4and to check their travel plans for Tuesday morning, January 5.
"An indefinite train driver overtime ban is also currently in force which may impact some timetabled services until the dispute is resolved."
Gareth Thomas, HR director for Arriva Trains Wales, said: "We are extremely disappointed that the train drivers unions have not accepted our latest offer of improvements to terms, conditions and pay for their members, and that they have opted to take industrial action, even though we submitted a revised proposal to them on December 23, following productive pre-Christmas talks.
"Directors at Arriva Trains Wales have been in contact almost every day with union officials in a bid to resolve this issue and stress the urgency of the situation if disruption to customers was to be avoided."
The union denied company claims that a new offer had been made.
Simon Weller, Aslef's national organiser, who is leading negotiations for the drivers, said: "The company has not made a new offer. It has sent us a form of words. But it is not new and it is not an offer."
Aslef said it was available for talks to resolve the dispute but added there was nothing at the moment to discuss. The pay side of the dispute has been accepted but Aslef claims the company is trying to "railroad through" changes to terms and conditions.