The Psychiatric Nurses Association is warning of further closures to beds and wards in the country's hospitals today.
Its members are refusing to work overtime as part of their dispute with the Health Service Executive over compensation for nurses who are attacked at work.
Mental health services across the country are being badly affected by the overtime ban.
Yesterday beds in Tallaght and St Vincent's hospitals in Dublin and Naas General Hospital in Co Kildare were closed.
Des Kavanagh of the PNA says he expects whole wards to close over the coming days because of the dispute.
The PNA and SIPTU are to meet on Tuesday next to decide if they will escalate the industrial action.
In a statement, the HSE said it was disappointed that the unions had taken an action that was designed to disrupt services and limit the care provided for mental health patients.
It said it was working around the clock to provide as full a service as possible.
