The Public Service Association says a substantial number of redundancies may result from fresh restructuring at the Ministry of Health.
Uncertainty surrounds the future of many jobs at the ministry, which is introducing a new policy advice structure in February.
Eighty-nine current policy advisers have to apply for a total of 90 jobs, only 60 of which involve pure policy advice.
PSA national secretary Brenda Pilott says 150 of its members are affected.
The ministry says it's too early to say how many redundancies there will be, but the overall number of staff will remain largely unchanged.