The Psychiatric Nurses Association will begin balloting its members today for industrial action up to and including strike.
It is the latest nursing union to poll its members in the ongoing row over the recruitment and retention crisis in the health service.
The union's national executive committee is recommending members vote in favour of industrial action in the ballot, which will take around three weeks to complete.
PNA General Secretary Peter Hughes says they've been left with no other option:
Mr Hughes said: "In the mental health services, for example, we did a survey of our branches last November and there were 500 vacancies.
"We did one at the end of August this year and there are now 700 vacancies, that is a 40% increase in the vacancies, so the situation is not getting any better, it's actually exacerbating.
"Month on month we are losing staff."
- Digital Desk