Around 7,000 hospital support staff, including 1,000 chefs, could go on strike in a row with the government over pay.
SIPTU is to ballot the workers, including healthcare and maternity assistants, those working in labs, and Surgical Instrument Technicians, next month on industrial action.
The union says many of them are entitled to pay rises of between 5 and 7 per cent since last October, under a Job Evaluation Process as part of the Landsdowne Road Agreement.
Separately, 1,000 hospital chefs, who are members of the union, want a review of their pay.
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