Premier Dominic Perrottet is under mounting pressure to sack the deputy Liberal Party leader amid the seven-week scandal over how Mr Barilaro landed the $500,000-a-year trade role he created when he was a minister.

Documents released to a parliamentary committee probing the controversial appointment have raised serious questions over the recruitment process.

Other documents, which are yet to be produced weeks after the parliament ordered them, could delay the committee's inquiry.

General counsel from the Department of Premier and Cabinet and Department of Enterprise, Investment and Trade could be called before the inquiry to explain the delays, Labor committee member John Graham said on Tuesday.

Investment NSW CEO Amy Brown, who has borne the brunt of the blame for Mr Barilaro's appointment, is expected to return for further evidence at a hearing on Wednesday, but could be called back for additional future hearings, due to the delay in documents being provided.

Mr Ayres insists Mr Barilaro's appointment was made by the public service but conceded on Tuesday he should have anticipated the political damage the appointment would create for the government.

"I should have told him that even though he's a private citizen, and he can apply for the role ... it was probably not in his best interest or the state's best interests," Mr Ayres told reporters.

"Given what Mr Barilaro has been through, he too would seriously question whether applying for this job was in his best interests."

Mr Ayres also said he wasn't encouraging Mr Barilaro to apply when he sent him a copy of a reposted job advertisement in December, which he did not send to anyone else.

"I was merely informing him the ad had been published," Mr Ayres said.

The opposition says the latest files - which indicate Mr Barilaro was not initially considered the best candidate before his assessment was upgraded and those of his main rivals downgraded - put pressure on Mr Ayres to explain himself.

Labor's treasury spokesman Daniel Mookhey said it was clear Mr Barilaro had been given preferential treatment.

"Every hurdle in the way of John Barilaro getting this job was mysteriously removed," Mr Mookhey said on Tuesday.

"He's either the luckiest person in NSW or it's clear that the process was retrospectively changed."

Mr Barilaro walked away from the role less than two weeks after his appointment was announced in June, saying it had become untenable.

Several coalition ministers have declined to publicly support Mr Ayres, who admitted one colleague had asked him to quit, although the premier had not.

Mr Perrottet is waiting until a Department of Premier and Cabinet review into the former deputy premier's appointment delivers its findings before taking action.

Mr Ayres maintains he's done nothing wrong but agrees his position will be untenable if the review disagreed.

The opposition is concerned about the government's review because it won't have access to the same documents as the upper house committee inquiry, which can also compel witnesses to testify.

"We don't believe that it's been an inquiry, we believe it's an administrative review," Labor's upper house leader Penny Sharpe said.

Australian Associated Press