Junior doctors are accusing their employers of wasting millions of dollars coping with strikes over their employment contract.
Members of the Resident Doctors' Association are to go on strike for five days from Monday.
They have already held four two-day strikes since mid-January.
The union said details released under the Official Information Act showed district health boards spent $15 million on healthcare workers, including senior doctors, to provide cover during the strikes.
Re-scheduling operations and other services cost Auckland DHB more than $1.5m, the union said.
Health boards said strikes always created costs and these would be avoided if the union cancelled the next strike.