Industrial action by radiographers has now spread to 14 district health boards, but their union says patient welfare will be minimally affected.
The union, APEX, began action at five district health boards in February, after unsuccessful negotiations for a 3% cost of living wage increase.
APEX national secretary Deborah Powell says it is unfair radiographers have not had a pay rise considering what she says is proven productivity and an increase to DHB funding.
Dr Powell says as the strikes are partial at this stage - including refusal to answer phones, no overtime and work-to-rule action - patients are unlikely to suffer.
However, she says if an agreement is not reached with the DHBs then there will be a complete strike, which will affect patients.
DHB New Zealand spokesperson Phil Cammish says radiographers' salaries range from $46,000 to $63,000.
He says they are well paid compared with other occupations that require similar qualifications for entry.
Mr Cammish says radiographers received a 3% increase last March and APEX's demands would increase the DHBs' costs for radiographers by 15%.
Boards say contingency plans are in place.