The Department of the Prime Minister and Cabinet bought $70,000 of ''human resources'' advice from a Canberra consultancy to help with its downsizing program between March and June.

The spending, another example of Canberra's private sector profiting from the public service jobs cull, has drawn fire from the opposition, which has accused the government of ''twisted priorities''.

The elite department's average staff is being slashed by up to 400 out of a workforce of 2418, after deep funding cuts inflicted by the federal budget.

A ''spill and fill'' process, forcing public servants to apply for their own jobs, will be used at several units in the department after calls for voluntary redundancies failed to meet the job loss quotas.

In an answer to a question on notice from Labor finance spokeswoman Penny Wong, the department said it had hired QMS to advise on a ''range of matters''.

''QMS is providing strategic HR [human resources] advice on a range of matters including enterprise bargaining, the voluntary redundancy and downsizing process and structural changes,'' the PM&C statement said.

But Senator Wong was critical of the consultancy.

''This is an example of the Prime Minister's twisted priorities,'' she said.

''While staff and services are being slashed, the Prime Minister is paying $20,000 a month for private sector 'strategic HR advice'.''

A spokesperson for the Department of Prime Minister and Cabinet said QMS had been paid only $4620 to date and was providing strategic advice to the department in the form of specialist change management support.

''These services supplement internal capacity or provide specialist services that the department does not perform in-house,'' the spokesperson said.

The highest-ranking PM&C staff targeted for departure are 30 band-one executives, who receive base pay of more than $170,000 a year, in the indigenous affairs section.

One in three will lose their job.

A Senate estimates hearing heard in May that the vast majority of these staff, and others facing potential job loss at the department, had recently been transferred into the organisation from other departments.

A total of $25 million was due to be used to cover redundancies at the department in 2013-14.