Talks are underway at the Labour Relations Commission in a bid to avert industrial action at Irish Rail.
Management and unions are meeting to discuss the row over driver pay and conditions.
The National Bus and Railworkers Union says it fears for the safety of drivers following a reported increase in the number of violent incidents.
General Secretary Dermot O'Leary says industrial action is a real prospect.
He said: "Unfortunately it is extremely likely unless the company change their emphasis for future to past, that is the first thing.
"The second thing I have to say again is that the Government have a responsibility. You can't strip out funding for a public transport service and expect things to operate as normal."