The Psychiatric Nurses Association (PNA) has issued notice of industrial action to the Heath Service Executive in a dispute over staffing numbers.
The action will commence on 26 March and will initially take the form of a work-to-rule.
The PNA has accused the HSE of failing to exempt mental health services from proposed cuts in nursing numbers and restrictions on recruitment.
The union said that staffing in mental health services has been reduced to unsustainable levels impacting service delivery.
"The reality of the HSE Pay and Numbers Strategy is that it is a blunt instrument which will effectively wipe out over 700 vacant psychiatric nursing posts from mental health," PNA General Secretary Peter Hughes said.
"The current level of staffing shortages has left services hugely reliant on overtime and agency to maintain basic services and is severely impacting on service development," Mr Hughes said.
Yesterday, Fórsa, the Irish Nurses and Midwives Organisation (INMO) and Unite, served notice of industrial action to the HSE in a dispute over staff shortages.
The unions have accused the HSE of imposing recruitment restrictions and of suppressing posts.
The industrial action will begin on 31 March following a three-week notice period.
It will initially take the form of a work-to-rule and other non-cooperation actions.
The unions have warned that other phased action, including work stoppages, will be considered should there be a requirement to escalate the dispute.
Health Service Executive CEO Bernard Gloster said the planned industrial action is "regrettable" against the background of additional funding for the health service and increasing staff numbers.
Mr Gloster said he expects to recruit 6,800 more people before the end of the year.
The HSE has said its Pay and Numbers Strategy has enabled it to stabilise its workforce numbers and has allowed it to increase staffing levels.
A HSE spokesperson said any industrial action would be seriously disruptive to the provision of services and will lead to increased delays and longer waiting lists.
"The HSE will seek in every way possible to have this action avoided," the HSE said.
PNA Deputy General Secretary Michael Hayes said the industrial action is "going to highlight the large amounts of goodwill that our members actually place into the system every day and the over reliance on the agency and overtime within the system."
Speaking on RTÉ's Morning Ireland, he said: "I suppose we don't want any impact on patients, but the long-term reality of the PN numbers strategy as it's currently designed would suggest that we're going to lose hundreds of nurses out of the system if the reductions in agency and overtime envisaged...were actually to take place."
