Psychiatric nurses across the country are to be balloted on industrial action up to and including strike.
The Psychiatric Nurses Association (PNA) announced the move in response to staffing shortages.
The union said there were more than 600 vacancies nationwide with 58 additional workers needed in the intellectual disability service in the north Dublin area alone.
The PNA said it had no faith in the HSE's ability to put a proper nursing workforce in place.
The ballot will take two weeks. The union's national executive committee has recommended a vote in favour of action.