The industrial action would involve 10 medical physicists employed at the Southern District Health Board, union advocate David Munro said.
‘‘They absolutely hate to do this but they feel they have no choice.’’
The Apex union represents 90% of the 80-strong workforce nationwide.
Apex members plan to walk off the job for 24 hours on Friday and again the following Monday and Tuesday.
Those stop works will be followed by two weeks of physicists only supporting radiation treatment during ordinary working hours.
The combined DHBs had refused to offer an immediate pay increase to the physicists, which given the impact of inflation meant that their pay offer was effectively a pay cut, Mr Munro said.
‘‘A chief physicist in New Zealand is only paid the equivalent of a newly qualified physicist in Australia.
‘‘We have been working to stem this ‘brain drain’ for more than a decade, and our system simply cannot continue to undervalue this workforce.’’
SDHB medicine, women's and children directorate general manager Simon Donlevy said the board had yet to establish how many patients could be affected by the action.
‘‘At this stage we are still working to understand the extent of the impact of the upcoming strike on our services.
‘‘We are prioritising all urgent cases to ensure they are not delayed.’’