INDUSTRIAL action is due to begin today at hospitals across the north as healthcare staff protest over pay and staffing levels.
Members of the Unison and Nipsa unions begin industrial action short of striking today over issues that also include mileage rates.
Nipsa has said the issues "go to the very heart of defending our members living standards and ensuring we have a health service into the future".
Unison meanwhile, said its members were "frustrated and angry that once again they are being left behind and are now the lowest paid part of the UK NHS workforce".
Unison members will also hold a day of strike action next Monday December 12, while the Royal College of Nursing (RCN) is to hold two days of strikes on December 15 and 20, with services including paediatric intensive care, chemotherapy and dialysis exempt from the action.
Speaking of this week's action short of striking, Nipsa has said it recognises "this is likely to be the strongest industrial action ever undertaken in the health service".
A spokesperson said: "With that in mind, patient safety remains a priority for NIPSA. Discussions have already begun to ensure the employers take the necessary steps to protect patients during the dispute."
Nipsa members voted 92 percent in favour of strike action and 97 percent for action short of striking during a ballot.
Health trusts across the north have said they are preparing to manage the impact on services and would update the public accordingly.
When announcing details of both this week's action short of striking and next Monday's strike, Unison's Anne Speed warned the "cost of living crisis is biting deep" for healthcare workers in the north, and said that unless the issue of pay was resolved "staff recruitment and retention will spiral into further difficulty".
People Before Profit MLA Gerry Carroll said those taking part in the action "have my full support in their fight against low pay and unsafe staffing".
"Unions gave political leaders every opportunity to avert the upcoming strikes. They protested, they lobbied, and they warned about the urgent need to put health workers' pay right," he said.
"Consistent cuts are fuelling the privatisation of healthcare and driving staff away from our health service. Health workers have been given no choice but to strike to defend the NHS."
Meanwhile, the head of the RCN has hit out at comments by UK Conservative Party chair Nadhim Zahawi linking strike action to the Russian war in Ukraine.
Mr Zahawi said Russian president Vladimir Putin's war was behind rising costs, and told Sky News on Sunday: "This is a time to come together and to send a very clear message to Mr Putin that we're not going to be divided in this way...our message to the unions is to say 'this is not a time to strike, this is a time to try and negotiate'."
RCN general secretary Pat Cullen, the former director of RCN Northern Ireland, described Mr Zahazi's comments as a "disgraceful".
"Using Russia's war in Ukraine as a justification for a real-terms pay cut for nurses in the UK is a new low for this government. The public does not believe this kind of rhetoric," she said.