Talks are expected over the weekend to avert the threat of renewed industrial action on the DART over the redeployment of three drivers.
The DART drivers have already been paid £8,000 each to allow new drivers to be trained and to extend the service to Greystones.
Eight new drivers are now available and the company had hoped to deploy all of them on Monday.
It had not anticipated this would cause problems because the service is short five drivers and a further three are needed to commission new rolling stock. But after DART drivers rejected a new pay deal on Thursday the three existing drivers who had volunteered to commission the new rolling stock withdrew their offer. The drivers have decided that only five of the eight new drivers can be deployed.
The human resources manager of Iarnrod Eireann, Mr John Keenan, said last night the company intended using all eight.
SIPTU branch secretary Mr Tony Tobin said drivers had rejected new pay proposals by an overwhelming vote. The Labour Relations Commission was available for talks and the company should use its services rather than act unilaterally.