A majority of orderlies working at Waikato Hospital were due to walk off the job for 24 hours from midnight on Thursday.
Seventy-two orderlies from a staff of 112 are taking industrial action over pay and conditions.
The Unite Union's Waikato-Bay of Plenty organiser, Jared Philips, says his members are frustrated and believe industrial action is their only option.
Mr Philips says in the past, action has been restricted to two-hour stoppages but the workers are now at the stage of wanting to disrupt the hospital.
The district health board says the impact on patients and the public will be minimal and all essential and urgent services will be maintained.