Frustrations have "boiled over" after a long-running dispute over pay and conditions for hospital anaesthetic technicians.
Apex, the union representing these workers, was currently trying to reach an agreement with individual district health boards.
Two strikes are planned in Northland next month, and technicians in Hawke's Bay are due to walk off the job for 24 hours next Friday.
Apex said Mid-Central DHB technicians were considering an offer, but strike action could also be on the cards at Lakes District and Southern DHBs.
Hawke's Bay chief medical and dental officer of health Dr John Gommans said patients booked in for surgery next Friday would now have to wait days or even weeks for their surgery.
"At the moment, we've had 13 people who are already booked for that day who have been notified that their surgery has been postponed," he said.
But Dr Gommans said emergency surgeries would not be affected by the strike.
Union national secretary Dr Deborah Powell said it had been trying to sort out pay and conditions all year.
"It would be fair to say the frustration has just boiled over at the failure of the district health boards to seriously address the problem," she said.
She said there was also a shortage of workers.
"Up in Northland we have five out of 19 positions vacant, there is quite a strong incentive to leave district health board employment and work in the private sector," she said.
Dr Powell said anaesthetic technicians could earn around $20,000 more in the private sector.
She said she was hopeful of a resolution and pay rises would be calculated differently for each region.