All Arriva Trains Wales services will be cancelled on Monday, January 4, because of a drivers’ strike.
The 24-hour walkout by members of the Aslef union is over a dispute on pay and conditions.
The industrial action will cause chaos for commuters, many of which will be returning to work after the Christmas break.
Drivers belonging to the Aslef union have also been refusing to work overtime during the last three days.
A spokesperson for Arriva Trains Wales said the strike may also affect early morning services on the following day.
They 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 4 and to check their travel plans for Tuesday morning, January 5.”
Aslef have said that a pay offer for their members had been accepted, but a change in their terms and conditions was at the reason behind the action.
A strike planned for November was previously called off.