The Labour Party has accused the Government of appointing spies in Government departments.
Finance Minister Bill English says the "private purchasing advisers" are assisting new ministers to trim Government department budgets.
In a series of answers to written questions, a number of ministers have confirmed they have hired purchase advisers, who are paid by their departments.
Mr English says ministers need people alongside them who are not part of the public service but understand state sector mechanisms.
The part-time advisers are paid for by the departments but answer to ministers.
Labour Party MP Chris Hipkins says that allows ministers to increase their staff without increasing their budgets.
The Public Service Association says it suggests the Government doesn't trust public servants.
The union's national secretary Brenda Pilott says political advisers should be paid for by the minister and the arrangement breaches the State Sector Act.
"In this case the advisers are clearly accountable to the Minister and not the chief executive of the department who is paying them," she said.
"That cuts right across the principles of political neutrality."
However, a spokesperson for the State Services Commission says the Commission doesn't believe the advisers are unlawful.
In a letter to ministers, Mr English said the purchase advisers would advise ministers on whether what their departments were doing was aligned with the Government's priorities.
He said the purchase adviser would be accountable to the minister but would work mainly from his or her own base, rather than being formally set up in a minister's office.