No trains will run on Valley Lines on Monday as Arriva Trains Wales (ATW) drivers strike in a row over pay and conditions.
No services will run to or from Barry, Treherbert, Merthyr, Aberdare, Rhymney, Coryton, Penarth and Cardiff Bay.
Monday's 24-hour strike was called after The Rail Maritime and Transport (RMT) union described ATW's pay offer as "paltry".
ATW apologised for the inconvenience to passengers.
It said it had also been unable to run services between Cardiff and Maesteg, Cardiff and Swansea, Cardiff and Ebbw Vale and Cardiff and Cheltenham Spa.
Cross country trains were calling additionally at Severn Tunnel, Caldicot, Chepstow and Lydney on the Cardiff to Cheltenham Spa route.
A statement on the company's website said: "Arriva Trains Wales is disappointed that RMT and its driver members have chosen to announce industrial action for 24 hours on Monday, 27 December despite the significant pay offer which has been made.
"Regrettably, due to this industrial action, no Valley Lines services will operate on Monday, 27 December and passengers are advised to make alternative transport arrangements.
"Arriva Trains Wales intends to run a full service on all other routes on the network.
"Arriva Trains Wales would like to apologise for the obvious inconvenience this will cause to passengers."
The RMT union said 85% of members backed the industrial action.
ATW said drivers had been offered a pay increase of 12% taking their basic pay from £34,824 to £39,117 in two stages.
The offer also changed the obligation to work on Sundays from a voluntary to a contractual basis, said the train operator.
It said train drivers were represented by two trade unions, Aslef and RMT, and that Aslef had recommended the latest pay offer to its members for acceptance.
RMT general secretary Bob Crow has said the offer would leave union members "out of pocket".
"Our members would have ended up with inferior working conditions for a de facto pay cut," he said.
"Arriva Trains Wales have shown us in the clearest possible terms that they have no wish to properly reward the hard work and loyalty to the staff and are motivated solely by the drive for bigger profits to line the pockets of the shareholders."