Talks between Iarnród Éireann management and unions are ongoing at the Workplace Relations Commission in a bid to avert possible industrial action by drivers.
The dispute centres on the mentoring of trainee drivers by qualified drivers, and alleged breaches of procedures by management.
The result of a drivers' strike ballot by the National Bus and Rail Union and SIPTU is due on 20 February.
Traditionally, mentoring was a voluntary activity but for almost the last two years drivers have refused to do it, resulting in over 30 trainees unable to complete their training.
According to management, this "trade union non-cooperation" has delayed career progression for the affected staff, as well as impeding expansion of commuter services and the introduction of a 10-minute DART schedule.
Drivers rejected a Labour Court recommendation which would have given them a 1.15% pay increase (over and above the 7.5% over three years awarded to the entire workforce) as well as increasing the daily mentoring allowance by a third in return for accepting that mentoring duties would be compulsory.
The company then announced it was implementing the Labour Court recommendation unilaterally, including paying the 1.15%. However, unions argue that this is an unacceptable breach of procedures.
The company has now advertised internally for drivers to express an interest in participating in mentoring.
Unions are also seeking negotiations on a shorter working week.