The Home Affairs department boss has skirted questions about Peter Dutton's decision to intervene and grant visas to two foreign au pairs.
The Home Affairs department has been accused of a "cover-up" over Peter Dutton's decision to intervene and grant visas to two foreign au pairs in 2015.
The visa status of au pairs was in the spotlight in March, when AAP revealed Mr Dutton used his powers of discretion as home affairs minister to grant visas on public interest grounds to two young women.
In the first case, an au pair whose visa was cancelled at Brisbane's international airport in June 2015 was able to make a phone call and within a couple of hours Mr Dutton approved a new visa.
In November the same year, he defied written warnings from his department that granting a visitors visa to a second au pair was of "high risk" because she had been previously counselled about work restrictions.
Department secretary Michael Pezzullo was grilled about the timeline of events during a Senate estimates hearing on Tuesday afternoon and took about 25 questions on notice.
Mr Pezzullo said he wasn't involved in the June 2015 au pair case.
Asked who the June au pair had phoned, Mr Pezzullo said he had no knowledge and took the question on notice.
Mr Pezzullo was repeatedly reluctant to discuss individual visa cases despite department officials commenting on Monday on the case of a Sri Lankan asylum seeker family swept up in a raid in Queensland.
"I prefer to apprise myself of the facts first before I contemplate giving any kind of information to the committee, probably on notice" he told the hearing.
Labor senator Murray Watt grew increasingly frustrated Mr Pezzullo was not attempting to find out the information from officials in the room, saying "it feels like a cover-up".
Why is it at every stage the blanket is thrown over questions over this incident?
Labor senator Murray Watt
"Why is it at every stage the blanket is thrown over questions over this incident?" Senator Watt asked, pointing to an AAP story stemming from a freedom of information case in which a federal tribunal ruled in favour of the department.
"Why the cover-up? ... The minute we get anything close to the minister the shutters go up."
Liberal frontbencher Mitch Fifield said he rejected the assertion.
Senator Fifield read out a press statement from Mr Dutton from late March which stated he doesn't know the two individuals involved and that they didn't work for his family.
The department declined to say how much it had spent on legal fees fighting the FOI case but would take the question on notice.
Mr Dutton's office has refused to answer specific questions about the identity of the au pairs' employers.
Mr Dutton had considered 523 cases seeking ministerial intervention this financial year and had granted 377 visas.
Some cases came directly through the minister's office or to the department or were raised by MPs.