Some 6,000 psychiatric nurses will resume their ban on working overtime on Wednesday.
It comes after talks to resolve a dispute between the Psychiatric Nurses Association (PNA) and the Health Service Executive (HSE) broke down on Monday night.
The dispute centres on the recruitment and retention of mental health staff and has been ongoing for over five months.
The HSE says it regrets the breakdown of negotiations with the PNA, and remains available to resume discussions.
A spokesperson for Health Minister Simon Harris says he would "encourage the PNA to use the industrial relations machinery of the State, as the employer side is willing to do, in order to avoid the action going ahead on Wednesday."
The PNA claims talks have made "little if any progress".
In some services, it says staff shortages amount to over 20% and there are 700 vacancies in mental health services nationally.
PNA General-Secretary Peter Hughes says nurses are irate and frustrated.
He says the decision to re-start the overtime ban is down to the lack of effort from management to resolve the issue.
"We have a mental health service in crisis, continually haemorrhaging staff to the private sector, overseas and a total reliance on overtime and agency, which is unsustainable to maintain services.
"So from Wednesday onwards, our members will only work contracted hours".