The union for public servants is warning that job cuts at the Ministry of Health means vital expertise will be lost just when the country needs it most.
Staff have been told a quarter of jobs - nearly 200 - are likely to go as the Ministry tries to find savings demanded by the government.
The PSA represents about 400 ministry staff and national secretary Kerry Davies said such a big cull was heartless and cruel.
It could also destabilise the health system, she said.
Details of exactly how the cuts would be made will not be revealed until April, with the Ministry saying some would be redundancies but others would come from leaving vacant roles unfilled.
Davies said either way, vital expertise would be taken out of the public health system.
"A lot of these people have been working for the Ministry and formed very strong bonds - particularly during the Covid period, giving their all to meet the demands of that pandemic crisis for New Zealand," she said.
It was naive of the government to suggest there was fat in the system that could be trimmed, especially with a growing and ageing population, she said.
"The work that is needed to prepare for the health needs of the country - that's really serious, important work. It's the backbone of the health system."
Staff were facing a great deal of uncertainty as they waited for more information, knowing they could lose a quarter of the people they work with.
"Not knowing whether that's you or someone you're ... working next to, that's a really big, big level of uncertainty and it's a huge cut. It's cutting really deep," she said.
The detailed proposal for change comes out in April, after which there will be three weeks of consultation.
The ministry's transformation management director Geoff Short said it was a difficult and unsettling time for staff.
Some of the proposed changes could also see new positions being created and restructuring was likely, he said.