Senior federal police have been quizzed over personal ties to staff at embattled consultant firm PricewaterhouseCoopers after Treasury revealed it had referred the firm for investigation.
The federal government on Wednesday night alerted the Australian Federal Police of the possible law breach four months after allegations first surfaced that then-head of international tax, Peter Collins, had shared privileged information on the Australian Taxation Office's multinational tax avoidance strategy with clients of the firm.
Greens senators also raised on Thursday morning whether nine ongoing contracts with PwC relating to its internal audit processes could cause a conflict of interest.
Australian Federal Police commissioner Reece Kershaw said he had the "utmost confidence" the right systems were in place to avoid any conflict of interest.
Senator David Shoebridge on Thursday morning quizzed the top cop about his friendship with former NSW police commissioner Mick Fuller.
Mr Fuller now works as a partner for PwC.
"I don't know if it's extensive in a professional capacity. He was a commissioner when I was a commissioner, and we've known each other for a number of years as police officers," Mr Kershaw said.
The Greens senator asked whether he considered Mr Fuller a "friend".
"Yes, but I consider all the commissioners are my friends, and retired commissioner," he said.
Mr Kershaw said he hadn't put in a conflict of interest declaration but did not reveal why.
He also admitted Mr Fuller had sent him a single text message since the PwC scandal broke, which revealed the former NSW cop had been "disappointed" in the firm.
The commissioner said he intended to provide a copy of the text message exchange to the committee.
Senator Shoebridge asked the commissioner if Mr Fuller had contacted anyone else at the AFP.
Mr Kershaw said he didn't know, and asked if he should query every employee in the force for clarification.
Senator Shoebridge earlier quizzed the law enforcement agency about its ongoing contracts with the big four consultant firm.
He asked whether it was an "inherent", "obvious" conflict of interest given the AFP has a $5.9 million contract with PwC for software and support services.
Senators were told there were appropriate confidentiality agreements in place and all contractors had been through security vetting processes.
The AFP was re-examining the contracts but there was nothing indicating any confidentiality breaches, the committee was told.
Mr Kershaw insisted he had the "utmost confidence" the right systems are in place to avoid any conflict of interest.
"I have the utmost confidence in our processes and our systems to not let any enter problematic intersection of those contracts or those arrangements interfering with or having that problematic intersection with a criminal investigation," Mr Kershaw said.
"We're very good at compartmentalising criminal investigations."
- with AAP