The Psychiatric Nurses Association says it looks increasingly likely that industrial action by its members and colleagues in SIPTU will begin next Wednesday.
Both unions have been campaigning for an improved compensation scheme for nurses injured at work.
They say that the present system is grossly unfair and offers either nothing or a monetary award of about one-fifth of what a person would get under the Personal Injuries Assessment Board.
Their overtime ban is due to begin on Wednesday and the General Secretary of the PNA, Des Kavanagh, admitted it would impact on patients.
However, he said they would strive to keep that to a minimum and blamed the Health SErvice Executive and the Government for what he said was their repeated failures to address the problem.
The HSE this evening urged the unions to explore industrial relations mechanisms before engaging in the action.
However, Mr Kavanagh said they had been through every mechanism over the last 15 years and still had not got a satisfactory resolution.
The issue will be raised with Minister for Health Mary Harney when she addresses the PNA annual conference in Trim, Co Meath tomorrow.
