The first wave of planned industrial action by health and social care workers is set to start on Monday.
Members of the union Unison including staff working in sterile services at the Belfast City Hospital and Antrim Area Hospital as well as support staff at the Ulster Hospital in Dundonald will stage walkouts.
Additionally all Unison members across the health and social services system will commence action short of strike.
The first phase of industrial action is planned to run to December 18.
It comes after talks with employers ended without agreement on Friday.
Unison regional secretary Patricia McKeown said the action is against "unjust pay and unsafe staffing levels".
"We know that the public is supportive of our campaign for pay justice and we ask that they show their support for their health workers today and in the weeks to come," she said.
"The beginning of industrial action must serve as a reality check to those in charge of the health service. They now must deliver for the public and the workforce."
On Friday the Department of Health said a formal pay offer was made which represents a 2.1% increase to the pay bill.
The department's Permanent Secretary Richard Pengelly said it was the best that could be afforded given what he described as budgetary constraints and amid the limited authority in the absence of a health minister at Stormont.
Meanwhile the Health and Social Care System (HSC) has issued advice to patients over potential effects of the industrial action.
"Trusts are working hard, where possible, to contact any patients and service users who may be impacted by any disruption to services or cancellations," the HSC said in a statement.
"All HSC organisations will continue to work closely together to mitigate the effects of any disruption.
"Information updates on patient services will be posted on trust websites and via social media over the next week."