The National Bus and Rail Workers Union have said there was no appreciable or significant progress at talks with Irish Rail management overnight.
Negotiations to try and avert industrial action on Friday adjourned shortly before 5am with no agreement.
The NBRU have said it has agreed to re-enter talks this afternoon in one final attempt to resolve the issues.
But it has described the past six days at the Workplace Relations Commission as long and frustrating and has said the union's commitment is not being matched by the company.
The row centres on payment for past productivity and if it's not resolved, drivers will refuse to work for three hours on Friday morning.