Members of the Psychiatric Nurses Association will strike in February in their dispute over pay and staff shortages.
The Association's 6000 members will refuse to work overtime on January 31, or on February 5, 6 and 7.
Industrial action will be escalated to full strikes on February 12, 13, and 14.
The union says recruitment and retention of nurses within the healthcare system needs to be addressed.
It's calling for "realistic proposals from Government as a matter of extreme urgency".
General Secretary of the PNA Peter Hughes says his members are overworked and underpaid.
"Our members are worn out doing overtime," he said.
"You can only do so much overtime and it's unsustainable to expect the nurses in the service to maintain the services as they are, and that's services standing still.
"There's no improvement in services so they're very frustrated."
Labour's Alan Kelly TD said the Labour Party fully backs the decision to take strike action next month.
"No worker takes going on strike lightly and the decision by PNA members to go on strike was obviously not an easy one to make," Deputy Kelly said.
"What we are seeing is that nurses are being asked to take on incredibly long shifts, and new recruits are being offered low wages."
He called on the Government to "show a bit of cop on" and discuss the issues with nursing representatives.
INMO members announced on Tuesday that they will strike on January 30, as well as February 5, 7, 12, 13 and 14 unless their pay demands are addressed.