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The union representing those staff, who perform MRI, X-ray and other scans, has given notice of two 24-hour stop-works, from 7am on September 30, and from 7am on October 2.
The staff had previously threatened to strike but last-minute negotiations averted the industrial action.
However, Apex union national secretary Deborah Powell said that deadline proposal by employers contained unacceptable changes to employment conditions for some staff.
"The offer also failed to address the particularly severe workforce shortages among those MITs with additional postgraduate qualifications in mammography, MRI and nuclear medicine."
Vacancy rates for MITs were as high as 25-30% in some areas, and staff could not cope any more, Dr Powell said.
"We can all work at above 100% efficiency for a time and when the need arises, but we simply can't work at that pace all the time, which is what is now being demanded of the MITs."
The Southern District Health Board employs 53 MITs at Dunedin Hospital, 28 at Southland Hospital and eight at Lakes District Hospital. All are union members.
SDHB chief executive Chris Fleming said services throughout the region would be disrupted if the strike happened.
"While we hope this strike can be averted, we still need to make plans for it, and these are under way."
That could result in some planned surgery and outpatient appointments being postponed, and patients would be notified if they were affected, Mr Fleming said.
"Anyone with a life-threatening situation will have access to the X-ray or scan they need.
"Patients coming to Emergency Departments who do not have a life-threatening situation will be assessed and treated by medical staff but may be required to come back at a later date to have a scan or be sent to a private radiology service for their X-ray or scan."