Iarnrod Éireann has already cancelled a number of services on its main routes due to the four-hour stoppage by rail and bus workers planned for later today.
The 11am and 1.20pm services from Dublin to Belfast and the 10.30am and 12.30pm services from Belfast to Dublin are all cancelled, as are the 11.30am Dublin to Waterford service, the 1.25pm Dublin to Rosslare train and the 6.20pm service from Rosslare to Dublin.
Cancellations will also be in force from 10.30am onwards on the Maynooth commuter routes.
All services between 11am and 3pm are expected to be cancelled due to the stoppage and further cancellations outside of these hours will be announced by the company as they arise.
Passengers have also been advised to expected severe disruption throughout the day.