Commuters in Dublin could be facing disruption to their daily travels next month after Luas workers voted in favour of strike action.
The SIPTU members have agreed to embark on industrial action in a dispute over their conditions of employment.
The union said the work stoppages and work to rule were expected to take place in February.
SIPTU organiser John Murphy said: "It's a fairly successful operation that transports thousands of people on a daily basis.
"The company has been profitable, and the members operating this system have not been paid to the degree that they would expect."