Train drivers are to ballot for strike action in a row over plans by Irish Rail to introduce a 10-minute frequency DART service.
The National Bus and Rail Union says DART drivers will be balloted on industrial action over Iarnród Éireann's planned implementation of a 10-minute DART frequency without the agreement of the union's members.
On Wednesday Irish Rail informed trade unions at the Workplace Relations Commission that they were going to move ahead with the plans without the consent of drivers.
Iarnród Éireann said senior trade union officials of NBRU and SIPTU "have preemptively sought conflict over service improvement by withdrawing from normal roster change processes".
Saying DART passenger numbers had increased by 8% in 2015, Irish Rail added: "We are working to deliver improved DART services to the public in response to increases in demand...The rosters we have proposed can be delivered within all existing rostering parameters, as the number of drivers is being increased through training to facilitate this.
"It is not a productivity issue at all, and trade unions are misleading both the public and drivers by claiming otherwise, as demonstrated by the company at Workplace Relations Commission conciliation this week."
The ballot is expected to be completed next week.