The Minister for Health has criticised the overtime ban imposed by the Psychiatric Nurses Association, describing the industrial action as "not on".
Speaking at the launch of a new policy on graduate nursing, Simon Harris said the overtime ban "needed to be called out for what it is".
He urged both sides in the dispute over staffing shortages to return to the Workplace Relations Commission to try to reach a resolution.
Mr Harris said there was now a "worrying trend" whereby trade unions were entering negotiations, and then staging industrial action in the middle of that process.
He said there was a mechanism in place to resolve the dispute, and said that further action should be suspended in the interests of patients.
Psychiatric nurses are taking industrial action, after their union said there had been a lack of progress with the Health Service Executive.
Minister for Health Simon Harris has criticised the overtime ban imposed by the Psychiatric Nurses Association, describing the industrial action as "not on". | https://t.co/xDkW0Zy88G pic.twitter.com/KUnoOYaMSD— RTÉ News (@rtenews) July 11, 2019
They are refusing to work overtime, in protest at what they say are ongoing and worsening staff shortages.
The overtime ban, which started at 7am today, does not affect child or adolescent mental health services.
General Secretary of the Psychiatric Nurses Association, Peter Hughes, said services have been impacted but that the union had no plans to suspend the indefinite ban on overtime.
Mr Hughes said some community services have been curtailed today, with some closed and staff redeployed.
Senior management have also been working on frontline services.
He said some psychiatric nurses have now been on duty for nearly 24 hours.
He said the union was willing to return to talks at the WRC, if meaningful proposals were put forward by the HSE.
Mr Hughes accused the Executive of failing to show good faith during more than five months of engagement.
The PNA has been trying to resolve the row with the HSE since suspending its industrial action in February to attend talks at the WRC.
The union said that despite over five months of engagement, little progress has been made in addressing ongoing recruitment and retention issues.
The HSE has warned the action will have a significant impact on mental health services.
It is assessing the situation on a service-by-service basis.
Speaking in the Dáil, Tánaiste Simon Coveney said today's action is a "serious development" and some people were "surprised at the decision" of the PNA to go ahead with it.
Sinn Féin's health spokesman Louise O'Reilly raised the issue during Leaders' Questions.
She said the HSE recruitment embargo was exacerbating the situation.
"At a time of crisis, this embargo has to end," Ms O'Reilly said.
Mr Coveney described the dispute as disappointing, but said progress had been made since engagement began at the WRC.
He said he understood the frustration of the PNA at the pace of progress, but urged members to reconsider their action.
"I am informed that genuine progress has been made, although it has been slow," Mr Coveney said.
He acknowledged that the sector was reliant on overtime.
Ms O'Reilly said Mr Coveney's response would do "absolutely nothing" to encourage psychiatric nurses to undertake overtime.
She also said if the Government had tackled the recruitment crisis, an overtime ban would have no impact.
"The service is effectively being run by overtime, agency and locum", Ms O'Reilly said, adding it was not the way to run our mental health service.
Additional reporting Edel McAllister