Tomorrow's planned rail strike looks set to go ahead after a union spokesperson said they have been left "totally frustrated" by negotiations.
Talks reconvene at the Workplace Relations Commission at 11.30am, after they were adjourned shortly at 3.15am this morning.
Siptu, the National Bus and Rail Workers Union and Irish Rail management are meeting to resolve a disagreement around pay for past productivity.
NBRU general secretary Dermot O'Leary said that they have been left frustrated by the negotiations so far.
"While on one hand, we're in the room discussing future productivity with the company negotiators - on return to the same room, maybe two-and-a-half, three hours, four hours later ... it would appear that the bar lifts," he said.
"In other words, the bar is raised all the time. So you can probably tell from my demeanour here, that we are totally frustrated."
Spokesperson for Irish Rail, Barry Kenny, said that they hope to resolve the issue by this afternoon, but as it stands they cannot guarantee rail services tomorrow morning.
"We don't want to put an artificial deadline, but we do want to give certainty and we would hope that it can be resolved, and resolved positively from a customer point of view, at some point during the afternoon today," he said.
"But if you get to a certain time and it looks like we're close, we're not going to artificially shut the process down at that point in time.
"But we would say, right now, we can't guarantee services tomorrow morning, and right through the morning, I would say."