Rail passengers in the south and south-west will be affected by an unofficial action by train drivers this morning.
Four train services will be disrupted. The 7 a.m. service from Tralee to Dublin will instead start from Killarney, with passengers in Tralee being transferred by bus to Killarney.
The 8.30 a.m. Heuston to Tralee train will end at Mallow, where passengers will transfer to a bus for the remainder of the journey.
The 9.15 a.m. Tralee to Cork train will begin instead at Mallow, with passengers transported by bus between Tralee and Mallow.
And the 6.35 p.m. train from Heuston to Tralee will end instead at Killarney, with a bus service continuing to Tralee.
All other services will operate as normal, said a spokesman for Iarnrod Eireann.
He said he was still waiting for details about how services could be affected for the rest of the week.
He said the situation would change from day to day, depending on individual rosters, but the south and south-west would remain the worst affected.
It is understood the unofficial action takes the form of drivers refusing to work an extra shift on their rest days, which had been agreed as an interim measure to ensure full services could operate until September, by which point extra drivers would be trained.
The decision to take the action was made last week after the Labour Court rejected a claim by mainline drivers for the same pay and conditions as DART drivers.
Another issue for the mainline drivers is the introduction of a new service on the Maynooth line.
Mainline drivers are represented by SIPTU and the National Bus and Railworkers Union (NBRU).
A SIPTU spokesman said the union was "pursuing these issues through established industrial relations machinery and it has not exhausted all possibilities yet".
He said that as it was an unofficial action, the union was advising its members to work as normal.