A union has serious concerns for staff members at Inland Revenue, and fears that up to 30 percent of its staff could be affected by a restructure.
The Public Service Association (PSA) said a document on IRD's proposed restructure shows "sweeping changes to staff rolls" as major changes to the tax system are introduced.
PSA national secretary Erin Polaczuk said "The loss of expert staff and the lack of certainty for workers reapplying for more simplistically modified roles means that important regulatory changes to the tax system rest on very shaky foundations."
"This could affect up to 4000 staff in varying ways at this stage of the restructure, and this has not been fully explained."
Ms Polaczuk said organisational changes will be made from February 2018, and that little transparency has been provided about possible reductions in staffing levels.
"There's a lot of vague, corporate rhetoric and the language of restructuring being used by IR management to hide the very real effects on expert staff," she said.
"Make no mistake - this proposal contains future commitments to reduce IR's workforce by 30 percent by 2021, and this is the first step in accomplishing that."
The union has raised concern about the effect that cost cutting could have on IR call centres, and their ability to pursue tax avoidance and compliance.
An IRD spokesman said it was stopping some services on Wednesday "so that all of its staff can hear about changes to the organisation".
In May, it was reported the Inland Revenue Department was looking to cut about 1500 jobs, and earlier that it was looking to reduce staff numbers by about 30 percent by 2021.
PSA National Secretary Erin Polaczuk spoke to Duncan Garner.
Watch the video for the full interview.