Some Arriva Trains Wales staff will strike at Christmas
Some staff at Arriva Trains Wales will stage a 24-hour walk-out in a dispute over pay and conditions.
The planned action will take place on 27 December and is expected to hit travellers returning from their Christmas holidays.
The Rail and Maritime (RMT) union said action was necessary to force a rethink on a "de facto" pay cut by management.
Arriva Trains Wales (ATW) said it was in talks with the union and hoped to "resolve the situation".
It said it was "surprised and disappointed" at the move.
General Secretary Bob Crow said the work/life balance of drivers was not being considered.
The move threatens fresh disruption to passengers following the recent wintry conditions.
Staff at Arriva will walk out for a total of 24 hours after voting in favour of industrial action.
On Monday the union also announced that its members on Northern Rail are to strike on 27 and 28 December in a separate row over Bank Holiday pay.
Mr Crow said: "With the action now on it is down to Arriva Trains Wales management to get back to the table to seriously negotiate a pay offer which improves the work/life balance of drivers and which properly rewards their staff."
After the strike vote result was announced last week, Arriva Trains Wales said it was "surprised and disappointed".
It said the RMT had chosen to ballot for action "based on a previous pay offer which has since been superseded by a significantly improved offer".
On Tuesday it said: "ATW remains available for discussions with RMT and hopes that this dispute can be resolved.
"RMT represents only around 20% of the 620 Arriva Trains Wales drivers and of these only 52 drivers voted for a strike.
"Should industrial action on Monday proceed, we are hopeful that the effect on services can be kept to a minimum.
"ASLEF, the union who represents the majority of Arriva Trains Wales drivers, has recommended that the pay offer should be accepted by its members."
ATW provides services across Wales but the strike could also affect those living in Cheltenham, Gloucester and the Midlands where some services terminate.