Dart drivers will decide today whether to accept a Labour Court recommendation to drive longer trains for no extra pay.
They are seeking a 9 ½% increase in basic pay for operating the longer trains because they say they are increasing productivity.
Drivers at the top end of the pay scale earn €48,000 approx per annum, for a five-day 41 hour week.
Iarnród Éireann say that the driver's claim has already been accommodated in a pay deal agreed in 2000 and the Labour Court has upheld its position.
However, Siptu, the trade union representing some of the DART drivers, says that the Labour Court recommendation did not rule out a lump sum payment. Iarnród Éireann has rejected that claim.
The company urged DART drivers to accept a Labour Court ruling and commence scheduled commissioning of 8-carriage DARTs from today.
If the drivers reject the recommendation, they will then ballot for industrial action. This could lead to disruption of Dart services in coming weeks and affect thousands of commuters.
Irish Rail has spent €250 million over the last two years upgrading the Dart system and lengthening station platforms to carry more passengers in longer trains.