The strike will involve more than 900 pathology staff nationwide, and about 200 in the Otago-Southland region.
It comes as pathologists in the private sector, including Dunedin's Awanui Labs, protest against the lack of pay parity with staff working for Health New Zealand Te Whatu Ora.
Apex union head delegate Sammy Heimseth said the difference was as high as 25% for some private providers.
"These private employers have fallen behind the times in terms of the cost-of-living adjustment in recent years.
"We've put out membership surveys and what we've received back is quite shocking.
"We're seeing sort of in the ballpark of 80% of members have experienced a significant amount of fatigue in the past 12 months.''
HNZ Living Well director Martin Hefford said extensive contingency planning was under way to manage and minimise any impacts on hospitals and community-based health services from the private laboratory strikes.
"All our hospitals and emergency departments will remain open, and we are liaising with the private laboratories to ensure patients who require urgent and critical care receive the services they need, including testing carried out at hospitals and in the community.''
NZ Pathology chairman Dr Peter Gootjes said it was attempting to "minimise'' the "disruption'' the strikers were going to cause.
Dr Gootjes said during the strike, community sample collection would be unavailable across all of South Island, and would be significantly affected across most of the North Island.
"Some services may remain available. However, it will likely be delayed and patients should expect longer wait times at available clinics.
"We recommend people defer non-urgent testing until the following week or contact their GP if they have concerns.''
Dr Gootjes said no laboratory support was available for elective surgery, which meant a significant increase in risk, delays, and potential complications.
"We understand the concerns raised by Apex members and recognise the challenges posed by pay discrepancies following the previous government's pay equity settlements for public sector employees.
"We are committed to working constructively with government and officials on this matter.''
The strikes will run for 24 hours on February 5 and 7 , but laboratory services will be affected for three days because of Waitangi Day.
Mr Heimseth said the simple message was that it needed to be "same work, same pay''.
"We have situations like in Christchurch, for instance, where you've got privately owned laboratory workers employed in a community laboratory doing ostensibly the same work as that of a public laboratory 20, 30 minutes down the road.
"Yet the difference in their work conditions is worlds apart and it can't go on for much longer like this.''
