Nurses have issued a strike notice to District Health Boards (DHBs), in preparation to walk off the job for 24 hours from 7am on July 5.
Both the nurses and the DHBs say they still hope to resolve the industrial dispute.
Hospitals and clinics around the country have begun preparations for the strike. The DHBs say a second strike notice for July 12 is expected to be issued next week.
DHB spokesperson Helen Mason says they are doing "everything they can" to avoid the strike.
"We're in mediation with the NZNO on Friday and in the interim, DHBs will start implementing contingency plans to ensure the safety of patients and staff."
There will be "significant changes" to DHB health services in the event of a strike, the DHBs say.
"Our aim is to keep everyone safe during the strike - patients and staff alike - and that means significant changes to normal services. Each DHB will be in touch with their affected patients to provide more information on this."
The strike is likely to see 27,000 nurses stop work. If it goes ahead, it will be the first nurses' strike in nearly 30 years.
Ms Mason said people should not avoid calling 111 or visiting a hospital with urgent matters. For non-urgent matters, people are encouraged to visit their GP, local pharmacy or call Healthline on 0800 611 116.