The Psychiatric Nurses Association is calling for its members to be prioritised for PCR testing.
The union estimates up to 600 nurses in mental health services are absent due to Covid-19.
The PNA says staff shortages are causing unprecedented and unsustainable pressures on remaining staff to deliver services.
Peter Hughes, General Secretary of the Psychiatric Nurses Association, says they need more support to keep services open:
"From a staffing point of view, I think what could help is to prioritise our nursing staff for testing and also to provide antigen tests would be helpful as well. We would hope that the situation doesn't get worse. I think there will be flows of people coming back on from duty and then maybe, unfortunately, other people having to be absent again due to COVID related issues."
