The ballot is expected to be completed next week
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 ten-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 fo drivers.
The ballot is expected to be completed next week.
Dermot O'Leary is General Secretary of the NBRU: