The Public Service Association says Department of Conservation workers are stunned by the extent of the looming job cuts, which it says threatens frontline workers.
The department is cutting 140 jobs in the latest round of restructuring, saying the changes will ensure it meets its $8.7 million savings target.
It says the changes won't compromise core services, with director-general Al Morrison saying the goal is for DoC to do its job more effectively.
Six new regions will replace the existing 11 regional conservancy boundaries.
This will result in the loss of about 118 regional management and administrative positions and 22 jobs in operational areas, including asset management and inspections.
But PSA national secretary Brenda Pilott says the cuts will affect frontline workers.
"Their title has been things like programme manager but these are people who work in frontline, very hands on, conservation work.
"These are not people who spend most of their time in an office dealing with paper. These are people who are out there on the front line of conservation."
Labour's conservation spokesperson Ruth Dyson agrees.
"What I have been told, from Department of Conservation staff who I trust, is that people who are involved in species recovery, track building and rangers now have their jobs under threat. I think they're frontline jobs."
The PSA also says staff are worried the cuts could lead to contracting out parts of the department's work.
Ms Pilot, says members are concerned about more work being shifted to the commercial partnerships DoC has set up.
She says Mr Morrison needs to convince a lot of people this new model is right.
Rangers safe - Minister
Conservation Minister Nick Smith says the jobs that will go are mainly in middle management and frontline ranger positions won't be affected.
"I made it quite plain to the director-general that while I was open-minded about a restructuring I wanted to see those frontline services, those rangers, protected and that is why we see all 99 of those field centres being maintained, going forward."
Dr Smith says the last time he was the Minister of Conservation, in the late 1990s, the department had fewer staff and a lower budget than it will have next year.
Forest and Bird says the distinction between frontline and management staff within DoC is misleading.
Advocacy manager Kevin Hackwell says the 118 positions classified as managerial staff are often project managers in the area offices.
"This is actually the people down in the local areas who are managing the various conservation projects that are going on and when they're not doing the management and administration they've got their boots on doing it.
"That's the sort of people we're talking about; the ones who are looking after the tracks, spraying the weeds, making sure the goats are being controlled."
Mr Hackwell says these cuts will mean more than 10% of DoC's staff have been cut in two years.