Irish Rail is appealing to graffiti artists to stop drawing on its trains.
Around €250,000 has been spent on removing graffiti from trains so far this year.
Trains right around the country are being hit, but it has become a major problem in the Dublin area.
The €250,000 figure only covers cleaning trains - more money being spent on removing graffiti from buildings, bridges and tunnels.
"If a train in graffitti'ed, and with our zero-tolerance [policy], the train has to be taken out of service," said Rita Butterly, corporate communications manager with Iarnród Éireann.
"Maybe those carriages have to be taken off and the train is smaller and leads to overcrowding on trains, and our customers aren't happy, so we don't want to have to do this."