The National Bus and Rail Workers' Union has warned of renewed disruption to rail and DART services in the New Year after Iarnród Éireann promised to introduce DART services every ten minutes from January.
The union said that the new rosters were "unworkable" and new services were proposed without consultation.
It said that the announcement put the company "on a collision course with drivers" and would only serve to "heighten tensions and run the risk of reigniting the recent conflict which led to industrial action and trains not running for a number of hours".
That dispute triggered a three-hour strike on the October Bank Holiday, though a second scheduled strike was called off at the 11th hour after unions and management agreed to attend the Labour Court.
A spokesperson for Iarnród Éireann said: "We are working to deliver improved DART services to the public in response to strong increases in demand.
"The rosters we have proposed can be delivered within all existing rostering parameters, as we have trained up new drivers to facilitate this - it is not a productivity issue at all."