The Justice Minister says "every effort" is being made to identify those behind an attack on a DART in Clongriffin.
A gang wearing balaclavas sprayed graffiti all over a carriage and threatened passengers with planks of wood on Tuesday night.
Irish Rail has described it as an "aggressive and calculated" attack on customers, and says it is the single biggest attack ever carried out on one of its fleet.
Speaking in the Dail, the Justice Minister Charlie Flanagan, described it as "completely unacceptable behaviour", that "will not be tolerated".
The Minister explained that Irish Rail is working with Gardai "to help identify the culprits", and stressed that "the type of behaviour we witnessed in Clongriffin this week has no place in civilised society".
Photos of the ‘graffiti tags’ are also being circulated in the hope of identifying any links with known graffiti offenders.