Ten nurses at the Acute Psychiatric Unit at University College Hospital, Galway have refused to go on duty this morning.
It is understood their protest is over concerns for patient care and staff safety at the Unit.
In a statement, the Psychiatric Nurses Association (PNA) said there had been 36 assaults on staff there since January.
It says there are continuing staff shortages at the 45-bed unit, leaving staff with no option but to protest this morning over concerns for their safety.
PNA national secretary Noel Giblin said last night's staff were still on duty.
"The night staff have satyed on duty," he said.
Of the overall issue on safety, he said: "Staff need to be found and the unit needs to be made safe. That has to happen, and talks have to happen."