Dart drivers who are members of Siptu have voted unanimously in favour of strike action if Iarnród Éireann presses ahead with new rosters without agreement.
The company plans to introduce rosters for a 10 minute service on Sunday, April 10th.
The National Bus and Rail Union (NBRU) and both Siptu have warned of industrial action.
The introduction of a more frequent Dart service is one of the key goals for Iarnród Éireann in 2016.
SIPTU Organiser, Paul Cullen, said: "Our members see the introduction of a 10 minute DART service as an issue which should be an integral part of discussions on increasing productivity. The failure of the company to effectively engage in such productivity discussions resulted in industrial action by all train drivers in Irish Rail during October and November 2015."
"Our members are deeply disappointed that the management of Irish Rail seems intent on provoking further conflict with workers. This is despite the Labour Court proposing a negotiation process which aims to create a forum where solutions can be found to productivity issues at the company.
He said introducing the new rosters would be seen by the drivers as a “deeply unfortunate and provocative move”.
In December Dart drivers who are represented by the NBRU and Siptu rejected proposed roster changes to facilitate the introduction of a 10-minute frequency Dart service.
The NBRU also contended that the introduction of a higher frequency Dart service will involve reductions in the lengths of existing trains as Iarnród Éireann has no additional capacity to put in place to facilitate the planned higher frequency service .
Iarnród Éireann has accused senior trade union officials of NBRU and Siptu of preemptively seeking conflict over service improvement by withdrawing from normal roster change processes.
