The opposition's assistant treasurer Andrew Leigh made the claim while hitting out at the appointment of incoming Treasury Secretary Philip Gaetjens, a former Liberal staffer.

"We are concerned that the coalition has been politicising treasury, using it much more as a Liberal party dirt unit rather than the eminent institution that it's traditionally been," he told Sky News.

He called the politicisation of Treasury "disgraceful".

Mr Gaetjens hit back at those who said he should never have been appointed to the role because of his Liberal links, saying public servants should be defined by their own capabilities.

He was a former chief-of-staff to Liberal treasurers Peter Costello and Scott Morrison.

He told The Australian Financial Review he was "more at the policy end of the spectrum than the political end".

"Certainly, there's a bit too much media focus on defining people by who they worked for rather than defining them by their own capabilities," he told the AFR on Monday.

"As most public servants would know, you do have to combine the art of the possible and look at what can be achieved in the politics of the day, which is getting more and more difficult."

Mr Gaetjens was also secretary of the NSW Treasury between 2011 and 2015 and served as a senior executive in the Commonwealth Treasury, the Department of the Prime Minister and Cabinet and the South Australian Department of Treasury and Finance.

Treasurer Scott Morrison has said Mr Gaetjens will bring "significant experience" to the job.

Treasury boss John Fraser will step down on July 31.

Australian Associated Press