The company is calling on NBRU to withdraw its proposal to ballot for industrial action
Irish Rail has written to unions proposing that all issues of concern be addressed at the Workplace Relations Commission.
Iarnród Éireann is urging the National Bus and Rail Union (NBRU) to withdraw its proposal to ballot for industrial action and have the issues dealt with by the WRC.
The company - which has also written to SIPTU and TSSA (Transport Salaried Staffs' Association) - says it has continued to engage with the WRC and Labour Court processes, despite withdrawals by some trade unions.
In a statement, Irish Rail says it is contacting the Commission in an effort to progress the range of issues and ensure service continuity and expansion.
The company says any WRC engagement "should be on the basis of the non-cooperation by DART drivers with in-cab familiarisation for trainee DART drivers ceasing, and that the NBRU withdraw its proposal to ballot for industrial action".
SIPTU and NBRU members at Irish Rail are believed to be looking for pay increases of around 25%.
SIPTU has referred a claim for "a substantial pay increase" for its members in all grades of the company to the WRC.
Iarnrod Éireann is attempting to increase its DART frequency, but postponed the plans last month. It came after unions threatened strike action over the plans to operate DARTs every 10 minutes.