Iarnród Éireann has told unions that it will proceed to pay an increase rejected by drivers but it will expect them to engage in mentoring of trainees, which they have been refusing to do.
It would have seen them receive a pay rise of 1.15% in return for past productivity and other concessions.
They included agreeing to mentor trainee drivers, which up to now has been voluntary.
For the last 20 months, the drivers have refused to do any mentoring, leaving 31 half-trained drivers unable to complete their training and qualify as drivers.
The refusal has also delayed developments including the delivery of a more frequent DART service and enhancements to commuter services.
In a letter to unions today, Director of Human Resources Ciaran Masterson informs them that, despite the rejection of the Labour Court recommendation, Iarnród Éireann will be paying the increase anyway with effect from 10 January but that mentoring trainees will no longer be voluntary.
The letter states: "Consequent on the 1.15% increase, driver's terms and conditions will be amended to reflect the fact that the mentoring of trainee drivers is a requirement of the role of train drivers, eliminating any suggestion that this task is voluntary in nature."
The drivers will also get a €31 allowance for any day allocated to mentoring.
However, Mr Masterson's letter does not specify when drivers will be scheduled for mentoring duties.
NBRU General Secretary Dermot O'Leary described Iarnród Éireann's position as "bizarre, disturbing and unprecedented".
He said it was unacceptable that the company would seek to change workers' conditions of employment without consent and warned that it would have to bear responsibility if any unilateral changes triggered a negative reaction among the driver cohort.