Bus Éireann services are set to resume in Limerick later today after drivers agreed under protest to end their unofficial work stoppage and return to work.
It follows a meeting locally with National Bus and Rail Union (NBRU) General Secretary Dermot O'Leary.
A meeting is now being sought with the Workplace Relations Commission and it is hoped it will take place this week to discuss drivers' concerns over a new roster for part-time or "spare" drivers.
Mr O'Leary said a nationwide ballot for industrial action - flagged with Bus Éireann management last December in the event that it went ahead with the new roster - is to go ahead over the next three weeks.
In a statement this morning, Bus Éireann said that was making every effort to resolve the situation and apologised to affected customers.
"We understand that a large number of our customers in Limerick depend on our services to get around including for work, education, shopping and hospital appointments," the company said.
"We are disappointed at this action and the impact it is having on our customers and we have urged those employees involved in this unofficial, illegal action to reconsider their actions and immediately return to work."
It is understood ten drivers took the action yesterday morning, the day a new roster was due to begin for 360 spare drivers in their workforce.
The company said it had been engaged for some time in a review of spare driver working arrangements and that an agreement on the new roster was reached and binding.
A spokesperson said the unofficial action came as a complete surprise considering the review of working arrangements has been completed.
It said the review was conducted through an extensive process that was jointly agreed between the company and trade unions and was facilitated by the WRC and experienced independent facilitators.
Bus Éireann said all parties agreed in advance that the determination of the assessors and the outcome of the review would be binding on all parties.
Mr O'Leary said the members "feel frustrated and are upset by a new regime that was forced upon them yesterday".
Speaking on RTÉ's Morning Ireland, he said that while the union did not have any official dispute with Bus Éireann, it "would not lambast members" who have taken action.
Mr O’Leary said that the union did advise the company a number of weeks ago "that they were heading into a situation where people would of their own volition take umbrage at being forced to do something that they say is not part of their conditions, despite the fact that we agreed on a report to be commissioned on our own spare duties".
He said that there is "complexity" attached to the issue.
Mr O’Leary said that the only way the dispute would be solved was in the WRC "where this whole issue started out".
He added that the union was not aware of the unofficial action taken by drivers.
Mr O'Leary said: "Unfortunately, my prediction has come to pass. So no, I had no knowledge of it."
Some 715 trips are operated from the city's main bus depot at Roxboro each week where 100 of the 213 drivers employed locally should have been working today.
Driver Michelle McInerney said that she did not want to leave passengers without a service but that she had no choice.
"It is a peaceful protest. Two buses have gone out of here this morning. We did not stop them. We did not stop any driver coming in in the car.
"We wish them well. We explained to them we are protesting over our rostering system. They understood that.
"Most drivers stayed below (in the depot), we did not ask them to, they decided that because every driver in this depot is fed up of being tread (sic) on and worth nothing. And that's what we are, we are worth nothing".
Driver Joe Enright said they had agreed to changes after the 2017 strike but they are now being asked to do things they had not agreed to.
"We had agreed to everything back in 2017 in the LRC - the document - but they are adding on bits the whole time and wanting change the whole time since, and this is the final straw what they are doing to us now, in fairness."
Bus Éireann said the new spare driver working arrangements have been implemented nationally with unofficial industrial action only occurring in Limerick.
The company said it was disappointed at the action and its impact on customers.