Laboratory workers, contact tracers and other critical health staff are planning to strike twice next month, after rejecting a pay offer from district health boards (DHBs).
But Public Service Association (PSA), the union which represents 10,000 workers, said it was the last option they wanted to take.
The workers want higher pay, equal treatment with other health professions, and action on safe staffing and retention.
PSA said unless health boards were willing to come back with a better contract offer, the two strikes would go ahead.
Union organiser Will Matthews said the planned strikes come after 15 months of "fruitless negotiations", and showed the depth of their frustration.
"We are now in a position where strike action is our only remaining option to get the DHBs and the government to listen, and to come to the table with an offer that ensures fair pay and treatment for our members.
"There are over 70 groups of workers who will take strike action: from laboratory workers - who are responsible for the swift testing and return of Covid-19 tests and Covid-19 contact tracers to sterile supplies technicians who clean and sterilise all surgical equipment prior to procedures - New Zealand needs each and every one of these professionals. And yet many of them don't even earn a living wage."
In a joint statement released on Thursday night, DHBs' employment relations spokesperson Rosemary Clements said DHBs were disappointed their latest pay offer was rejected despite being consistent with other pay settlements to health workers.
"We acknowledge the challenges in the health system and the pressure it puts on our people and to say we don't value our workforce is simply not true and not consistent with our approach to these talks."
Pay equity - one of the concerns raised by the union - was already being dealt with separately, Clements said.
They had also offered different ways to address concerns about the lowest paid, "including increases greater than the union is claiming", Clements said.
The health boards want the union to join them in applying to the Employment Relations Authority for facilitation.
"Facilitation will allow an independent third party with knowledge of the sector to help reach an agreement without disrupting patients, families and whānau, especially when we're facing an outbreak of the Omicron variant of Covid-19," Clements said.
"The sooner we can settle these pay talks, the sooner we can focus on their pay equity claim which is the proper place to assess and address the wider complex question of equity."
However, PSA delegate Dianna said the new DHB offer was "insulting".
"It felt like the DHBs only came to mediation because they had to but had nothing to offer in the hope of any resolution."
PSA member Leighton said many of the union's workers were burnt out and some could not even get leave.
"We are understaffed and over worked, and we have problems retaining staff. The final nail in the coffin is the message we have been sent that we are not as important or as valuable as the other professions in the health system."
Fellow member Nichola said the mental health workforce was also streteched from before the pandemic, and now they were "close to burn out".
"We feel disappointed and frustrated by the offer. We are being left behind while other health professions progress.
"We now have teammates working alongside one another earning significantly different amounts. We want fair pay, but the DHB offer doesn't reflect fair pay."
PSA has launched a petition calling on the government to make an offer that addresses pay, progression, retention and skill mix.