Members of the Psychiatric Nurses Association have staged a demonstration outside Galway University Hospital to protest at what they say are inadequate staffing levels there.
The association said patients and staff are being put at risk at the 45-bed acute psychiatric unit.
It said its members cannot provide proper care and that there have been repeated breaches of a staffing plan, agreed with hospital management.
The Health Service Executive said 12 staff have been redeployed from Ballinasloe to the acute unit in Galway in recent months.
A further eight new nursing posts have been approved, it said.
Agency nurses can also be hired to staff the unit if demand necessitates, the HSE added.
It said staffing levels at the unit are not static and fluctuate on a weekly basis, subject to various criteria.
These include the number of patients in the unit, the nature of their illness and their treatment requirements.