More than 800 administrative staff at South Island hospitals are to take industrial action this month.
The Public Service Association (PSA) says the workers, who include telephonists and secretaries, are striking because most of them are paid less than their North Island counterparts.
They plan to all take their breaks at the same time from 18 November.
That action will escalate to rolling strikes five days later if no progress is made.
The PSA says the South Island workers' salaries start at $27,000, while their northern counterparts earn at least $30,000.