The Psychiatric Nurses Association has announced its 6,000 members will strike in February in an escalating campaign of industrial action in their dispute over pay and staff shortages.
The psychiatric nurses will initially refuse to work overtime on 31 January and 1, 5, 6 and 7 February.
They will then escalate their industrial action to full strikes on 12, 13, and 14 February.
Previously, 95% of PNA members rejected Government proposals to address recruitment and retention issues among nurses.
PNA General Secretary Peter Hughes said the recruitment and retention crisis in psychiatric nursing was escalating on a monthly basis, with a 40% increase in vacancies between November 2017 and September 2018.
Mr Hughes described this level of vacancies as unsustainable, adding that it was seriously affecting service delivery and patient care.
He said the staff shortages needed to be addressed with realistic proposals from Government "as a matter of extreme urgency".
The 37,000 members of the Irish Nurses and Midwives Organisation announced on Tuesday that they will strike on 30 January, as well as 5, 7, 12, 13 and 14 February unless their pay demands are addressed.
The Government has repeatedly insisted that the €300m claim is unaffordable and would trigger knock-on claims across the public service.
Minister for Health Simon Harris has said he does not believe the industrial action is warranted and can be avoided.
In a statement, Mr Harris said there is a clear need for engagement and health sector management has invited nursing unions, including the PNA, to meet him next Tuesday.