The dispute at the Luas light rail system is set to escalate with drivers and traffic supervisors to consider balloting for an all-out strike in the next week.
Talks at the Workplace Relations Commission aimed at resolving the dispute broke down on Monday night after nearly 11 hours.
Siptu, which represents Luas staff, maintained the company had said it would engage in talks with only two grades - revenue protection officers and revenue protection supervisors.
The union maintained the company had declared it would not talk to drivers and traffic supervisors.
It said this was despite drivers effectively reducing by almost half the level of pay increases being sought.
Siptu divisional organiser Owen Reidy said drivers and traffic supervisors would now look at scheduling further strike dates.
He said both grades would also now consider a ballot on an all-out strike.
Mr Reidy said the earliest an all-out strike could go ahead would be in five weeks.
“There will be an escalation. Both those groups now plan further days of action,” he said.
“They’re going to have to consider a ballot for an all out strike. If it happens it would be ballot next week or so.”
Mr Reidy told Newstalk the drivers had been prepared to suspend work-to-rule indefinitely going into the talks on Monday.
“Essentially we’re talking about a pay increase that deals with productivity that’s going to happen over the next five years,” he said.
“After seven hours they get a slap in the face and told leave, we’re not talking to you anymore. What are they to do?
“But we now have an employer who has essentially broken off talks with two of the groups.”
Revenue protection staff will engage in talks with the company at the Workplace Relations Commission.
However, the union said they were still scheduled to take part in a stoppage planned for St Patrick's Day. Strikes at Luas are also planned for the Easter bank holiday weekend.
Luas staff earlier said they had significantly reduced the level of pay increases they are seeking.
Luas drivers had been looking for rises of up to 53 per cent over five years. However, according to some informed sources, the personnel concerned have scaled this demand back to about 6 per cent per year over five years.
Talks aimed at resolving the current dispute, which has already seen Luas services brought to a standstill for four days, reconvened at the Workplace Relations Commission on Monday.
Arriving at the talks, Siptu shop steward at Luas Richard McCarthy said the union had tabled a significantly reduced proposal. It appeared the new proposal had been “received quite positively”, he said.
He said the union had been asked to keep its new pay claim confidential for the moment.
Staff were looking for “meaningful dialogue” with management at the new talks , Mr McCarthy said.
Managing director of Luas operator Transdev, Gerry Madden, said he was looking forward to hearing the union's revised pay claim.
However, he said even if the pay demands were modified by 70 per cent or 80 per cent, “it would still represent a significant pay claim for any employer to deal with”.
The company had previously proposed increases of between 1 and 3 per cent, linked to productivity measures.