Christchurch Hospital has said it might have to postpone treatment for some patients, saying it would contact them directly.
That would likely be the case in some other hospitals, but Te Whatu Ora chief of people Andrew Slater said the agency would not know the full impact until after the strike had finished.
Health services would still be available for those who needed them, he said.
Senior doctors and junior doctors from the other main union would still be working, and would be providing essential “life preserving” services.