Iarnród Éireann have announced that 14 train services have been cancelled today, and two will be replaced by bus services due to a dispute over driver rosters.
The services disrupted today include afternoon and early evening services between Dublin and Drogheda, Sligo, Maynooth, Balbriggan and Clonsilla.
Iarnród Éireann said the ongoing breach of company-union agreements by some train drivers, which has caused intermittent disruption on a number of routes in recent months, is "unsustainable, and must cease immediately".
Talks between management and unions in the dispute have so far failed to resolve a number of issues, one of the main ones being the number of "rest" days that drivers are being requested to work on.
The company say some drivers are now defying "initiatives and instructions from the Labour Relations Commission, the independent facilitator for company-union talks on driver issues, and their own trade unions, SIPTU and NBRU".
The problem has escalated since a new timetable in January that has seen additional trains on several routes.
The company has apologised for the inconvenience caused and said it was due to a "breach of agreement" by unions. Drivers argue they have not been trained to operate new services.
Talks at the Labour Relations Commission have proved unsuccessful.
Fourteen train services were cancelled over the weekend and a number of others were replaced by bus transfers. Four trains on the Dublin Heuston to Cork line were cancelled.
The weekday 6.30 service from Portlaoise to Heuston and weekday 17.35 Heuston to Carlow service are cancelled until further notice due to the dispute.
The following services will be cancelled today:
13.38 Connolly - Clonsilla
14.10 Clonsilla - Docklands
15.40 Connolly - Maynooth
17.05 Maynooth - Connolly
18.08 Connolly - Maynooth
18.58 Maynooth - Connolly
12.30 Pearse - Drogheda
14.15 Drogheda - Connolly
14.45 Pearse - Balbriggan
16.16 Balbriggan - Connolly
17.07 Connolly - Balbriggan
17.48 Drogheda - Connolly
18.07 Balbriggan - Connolly
18.15 Pearse - Drogheda
The 16.00 Connolly-Sligo and 17.00 Sligo-Connolly services will be replaced by bus transfers.