Unions at Irish Rail are warning of a winter of discontent if agreement cannot be reached over a pay claim.
Talks get underway today at the Workplace Relations Commission, after being returned there by the Labour Court earlier in the summer.
The company says it is carrying major debts and cannot afford an increase.
However, the NBRU's Dermot O'Leary said that the union is simply asking management to pass on pay hikes in line with others in the transport sector.
"We're hoping the company will come to the table at least with some offer, and unfortunately if they don't, we see a situation where, certainly heading into the autumn, you could have a situation where there'll be a strike on our railways," he said.
"Look, the best thing we can all do to avoid that is to sit down and have sensible conversations.
"But if it doesn't happen, and the company continues with the line of the poor mouth, then unfortunately we are heading into a situation where there will be industrial unrest in the railway."