The Public Service Association (PSA) says a proposal to halve the Department of Conservation's Chatham Islands staff risks impacting front-line conservation efforts.
DOC has proposed to cut year-round staff on the islands from 11 to five, and merge the office with the Wairarapa district.
A boosted summer staff was also included in the proposal, which would see the on island team swell from five to 20 from October to April.
"Our members are feeling shocked and completely undervalued by this proposal," said Duane Leo, PSA national secretary.
"The staff are a passionate group of workers, who work all year round to support and protect more than 40 species that are on the endangered list Chatham Islands animals," he said.
Some of those species included the black robin, the Chatham Islands tūī, tomtit and warbler, and the Forbes' parakeet.
Protecting endangered species was not just a summer job, Leo said.
"Workers are concerned that this proposal puts vital work at risk. DOC staff also undertake much work co-ordinating volunteers, and others who are working to save endangered species and now that won't happen year round."
The proposal as it stood would undermine conservation efforts on the island, he said.
"While changes may be needed, these are wholesale changes, without consultation with interest groups who understand the challenges on the island."
Budget savings were not a factor in the change, DOC said.
Instead, it was in response to feedback from staff on the Chathams who had indicated their well-being was being negatively impacted under the current operational model, said Henry Weston, DOC's deputy director-general of regional operations.
Staff and the PSA now had until 22 May to explore alternative proposals with DOC during a consultation period.
A final decision would be made by the end of the month.