Irish Rail has warned of "significant delays" to services this morning due to "overnight vandalism".
Signalling equipment between Newbridge and Kildare was allegedly targeted last night, leading to huge issues for commuters today.
This could result in delays of up to 60 minutes on some routes this morning.
Irish Rail also warned that real-time departure information on their website and their App is likely to be incorrect due to the fault.
An spokesman wrote on Twitter: "Due to overnight vandalism of signalling equipment between Newbridge and Kildare, there will be significant delays to all services into and out of Heuston this morning.
"Delays of up to 60mins to all services are expected.
"Newbridge/Hazelhatch to Grand Canal Dock Services are also impacted by delays of up to 60mins due to the signalling problem caused by overnight vandalism of signalling equipment.
"Services from Heuston to Portlaoise will terminate at Newbridge in an effort to minimise delays to services into the city.
"Our App and realtime departures on the website takes its information from the signalling system.
"As a result of this, information for services into & out of Heuston and Phoenix Park tunnel services is not accurate this morning."
