Senior doctors say patients' lives will be at risk if the Wellington region's health boards privatise testing laboratories.
Doctors said they were fed up with a lack of consultation and have presented a formal document to board members, the Minister and Ministry of Health, and the region's mayors.
Auckland pathologist Jeanette McFarlane said laboratory staff were an invisible yet integral part of hospital care.
She was concerned the privatisation of these services could result in serious patient harms.
"If the laboratory services are privatised, I fear that these services that go on behind the scenes, and that close clinical link with our colleagues, will be compromised and that's to the detriment of patient care."
Dr McFarlane helped write a report for the Association of Salaried Medical Specialists.
Association executive director Ian Powell said the diagnostic work of hospital laboratories affected 70 percent of clinical decision making.
He said the bureaucrats leading the process did not know how hospitals and their clinics interacted.
Privatising the labs would potentially create hold ups in diagnosis and treatment for patients, he said.
"The consequences can include potential delays in cancer diagnosis, compromises in infection control leading to a further spread of illnesses, risks to safety and blood transfusions, affecting surgery and the management of emergency trauma cases, and a variation of the quality of laboratory results reporting."
He said the privatisation of laboratory services was the worst case scenario.
"We're going to have a tension on hospital laboratories trying to do the critical work they have to do for surgeons and physicians, while at the same time being under confused accountabilities and pressures to cut costs in order that the company can maximise their profits."
Mr Powell said the health board's own investigations showed the labs worked well and needed only minor improvements.
In a statement the chief executive of the Hutt Valley and Wairarapa district health boards Graham Dyer said he was convinced the consultation process had been robust.
"We are in the middle of a commercial process, so it would be inappropriate to discuss that process," he said.
"I am convinced that process has been robust and there are no issues with the process that has been followed."
Mr Dyer said while the current process was not broken, integration could save money and free up resources for other services.
The recommendations based on that process would be considered by the health boards in December.