A Labor senator has grilled Department of Finance officials as to why Assistant Treasurer Michael Sukkar's old law firm was used in an independent investigation into the minister.
Mr Sukkar and fellow Victorian MP Kevin Andrews were cleared of wrongdoing after an investigation into branch-staking allegations earlier this month.
While the department took part in the preliminary investigation, it was subsequently passed to law firm Ashurst Australia, where Mr Sukkar was employed as a senior associate between 2006 and 2013.
Labor senator Don Farrell asked finance officials if anyone was aware Ashurst was Mr Sukkar's former employer.
The department took the question on notice.
Senator Farrell asked why Ashurst was chosen.
Department executive David de Silva said Ashurst had the skills and availability to do the work.
"So there was only one firm of all of the law firms on this panel, all the law firms around the country, it ended up there was only one firm that could do this work," Senator Farrell said.
The department took on notice what other firms were considered.
"Can't anyone in the room see that something smells, when the law firm that gets selected to investigate the minister is the minster's old law firm?" Senator Farrell said.
"Maybe I'm the only one that thinks that, but I don't think I am."
Finance Minister Mathias Cormann objected to the senator's reflection on his department.
"You are now suggesting that somehow the department was motivated by anything other than conducting a proper independent review," Senator Cormann said.
Finance secretary Rosemary Huxtable said the services were procured through the department's legal services panel, and Ashurst had signed a contract declaring there were no conflict of interests.
Australian Associated Press