The head of the Workplace Relations Commission has rejected an accusation of bias against SIPTU, made against him by the union’s president, who also called for his resignation.

Commenting on the rejection by Luas workers of a proposed deal with Transdev following talks at the commission, WRC chairperson Kieran Mulvey called for leadership, saying that people need to understand when to depart the field having had considerable success.

SIPTU President Jack O’Connor called for Mr Mulvey’s resignation, saying he showed "bias against the unions" which renders him not credible as a mediator.

Mr O'Connor has since said that he regrets that he had to make the comments, but added they had to be said.

He said the focus should be on resolving the Luas dispute, saying the key to doing that was to listen to the workers.

The row comes as Luas workers go on strike for a further two days this weekend.

Mr Mulvey said this afternoon that he believed he was speaking in the public interest and had been trying to point out where the dispute could go.

He said that he saw no reason to stand down from his position.

Mr Mulvey said Mr O'Connor had made a personal attack on him but he would not descend to personal comments.

He said that "throughout its work in attempting to resolve the ongoing Luas dispute the focus of the WRC has been on bringing the parties together for discussions and to find an outcome that was acceptable to both parties and one that would bring to an end the not inconsiderable inconvenience being imposed on the citizens of Dublin and visitors to the capital".

Speaking earlier on RTÉ’s Morning Ireland, Mr Mulvey said: "We need to know what's wrong ... it's not an unending series of negotiations and maybe now we have to decide that we'll have a Luas five days a week in the future.

"We might have to live with a five-day Luas - that's what it is at the moment. In fact this week, it's a four-day Luas."

Mr Mulvey said that in his view it is "extraordinary" that no one has contacted him from SIPTU since the WRC proposals were rejected by its union members to explain why.

He said that most union officials who put forward the same proposal would receive a "standing ovation" from their members.

He questioned how a pay increase could worsen anybody's conditions of employment and said that most teachers, public servants and nurses would accept such a proposal.

Mr Mulvey also said it would be "absolutely disastrous" for Minister for Transport Paschal Donohoe to get involved in any pay dispute as this would undermine the role of the Labour Court and the WRC.

He said "leadership and judgement" is needed and that by any mark the proposals of the commission are "considerable".

He suggested the onus is on the workers who are disrupting the service to show this leadership.

Mr O'Connor accused Mr Mulvey of attacking one side in an industrial relations dispute - the workers - and said his continued presence as chairperson of the WRC would damage the integrity of the institution.

He said it has "quite clearly arrived at the time as the head of an independent, State-sponsored mediation service" where he must step aside.

He said that under Mr Mulvey's leadership he could not see that the WRC had any further role in this dispute and said the Labour Court, ICTU and Ibec may have roles to play.

He said Mr Mulvey's role in the dispute has been "curious" and questioned his "premature intervention" which he said resulted in a proposal that "no self-respecting union official" would accept.

He criticised Mr Mulvey for including a "ridiculous" proposal of new lower-level entry rates for Luas drivers, something Mr Mulvey earlier disputed was something he had put forward.

On the same programme, Mr Donohoe said Mr Mulvey and the WRC had his full support and the support of the Government.

Mr Donohoe called for calm in the dispute, describing it as having entered uncharted territory.

He said all sides involved should show respect for the WRC and the Labour Court and called for them to re-engage.

Mr Donohoe again reiterated that he would not be intervening in the dispute adding that it is not the responsibility of ministers to become involved in workplace disputes.

He said by intervening, it would "fatally" undermine both the Labour Court and the WRC.

Meanwhile, Transdev managing director Gerry Madden said that the only way the dispute can be resolved is if sensible pay claims are brought to the table.

Mr Madden said his experience of Mr Mulvey and the WRC has been positive, adding that the core of the problem is the pay claim and that a resolution needed to be found to that.

He said his door is open and that he is open to hearing pay claims that are in line with industry norms.

SIPTU negotiator John Murphy said there is a basis for going back into talks, but that the company had missed a number of opportunities to try to resolve the dispute.

Speaking on RTÉ's Today with Sean O'Rourke, Mr Murphy said Transdev CEO for Ireland and the UK Nigel Stevens should have met with unions and workers when he was in Dublin and said he was not aware of efforts made by Mr Stevens to contact Mr O'Connor.