Major restructuring is the "last thing" the health system needs, the Public Service Association says.
A review report on the health service suggested establishing a National Health Board to oversee and fund district health boards.
Health Minister Tony Ryall ordered the review in January and has received a draft report, The Dominion Post reported.
He was expected to release it for public discussion in the next few weeks before decisions are made about implementing its recommendations.
PSA national secretary Brenda Pilott said restructuring the system was no guarantee of further benefits.
"The last thing our health service needs is the upheaval and expense of another major restructuring.
"In fact, adding another administrative layer to the health system is more likely to increase the cost of delivering health services," Ms Pilott said.
A National Health Board would be similar to the former Health Funding Authority that was scrapped because it didn't work, she said.
The report warned of cuts ahead in the rate of growth in health spending - which Finance Minister Bill English signalled in his May budget.
It also calls for a debate about which health services should be provided by the Government.
Labour's health spokeswoman, Ruth Dyson, said a new National Health Board would mean another layer of bureaucracy and would be a re-run of the previous National government's policies.
She said Mr Ryall had consistently argued that there were too many bureaucrats in the health system.
