Medical laboratory workers say hospital laboratories in Wellington and Hutt Valley are archaic and need rebuilding.
The region's health boards are pursuing a proposal to merge hospital and community-based labs, bringing in private-sector involvement.
That is despite opposition from medical specialists and the withdrawal from the process of the community medical tests provider, Aotea Pathology.
The Medical Laboratory Workers Union said hospital labs in Wellington and Hutt Valley needed upgrading but faced funding constraints.
It said consideration of the proposal should continue with more input from clinicians.
The union's general secretary Deborah Powell said the merger would enable the boards to upgrade their hospital labs and ensure a sustainable lab service.
"Neither the Hutt or the Wellington laboratories are functional in a modern environment. We need new laboratories. Our people are at risk from all sorts of things - not enough space to run the machines, to do a proper job, all sorts of things in those laboratories at the moment."
But some senior doctors say DHBs in the Wellington region should abandon the proposal.
The executive director of the Association of Salaried Medical Specialists Ian Powell said the change was not in the best interests of patients or services.
"The risks of stopping it now are insignificant to the risks of continuing it on and that is what they need to do. They need to realise, look, for whatever reason we cannot continue going down this path."
Mr Powell said if the health boards made proper plans they would not need to turn to the private sector to help them upgrade facilities.
However, the chief executive of the Hutt Valley DHB Graham Dyer said a spinoff of the changes would be better public access to test results.
"In fact they should probably see an improved service, if we go ahead with it, given that there is a single repository and so there will be better access to test results for primary and secondary clinicians."
Graham Dyer said the boards would make a provisional decision on March 6.