With the votes of Labor, Centre Alliance, the Greens and One Nation on Monday afternoon, the Senate resolved to set up an inquiry into the roles, despite a departmental review finding no breaches of the ministerial standards.

Senator Rex Patrick pushed ahead with the motion after being dissatisfied with the review produced by Prime Minister and Cabinet secretary Martin Parkinson, and signaled Mr Morrison and Dr Parkinson could find themselves facing the committee.

Not long after the federal election, former defence minister Christopher Pyne announced he would be advising consultancy company EY (formerly Ernst and Young) on defence matters, while former foreign affairs minister Julie Bishop joined the board of Palladium in a non-executive role. Palladium has won almost $100 million in aid contracts.

Before the Senate vote, Labor had attempted to move the debate to focus on Ms Bishop, arguing a video filmed in the former minister's office during her time in the role showed she had dealings with the company as a minister, and she must be re-investigated. This was voted down in the House of Representatives, where the government flexed its new majority.

The departmental advice to the PM says the former defence and foreign affairs ministers' new gigs did not breach ministerial standards because while they benefited from their experience as ministers, they have pledged not to use knowledge from the roles.

The ministerial code of conduct says ministers must not lobby or have business meetings with politicians or public servants within 18 months of leaving parliament, on matters they dealt with in their final 18 months in office.

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Dr Parkinson's report on Mr Pyne and Ms Bishop found they didn't breach ministerial standards, but also told Prime Minister Scott Morrison there was no action that could be taken against former ministers either way.

"A distinction should be drawn between experience a person gains through being a minister and specific knowledge they acquire through performing the role. It is the latter that is pertinent to the standards," Dr Parkinson said.

He warned the former ministers should be careful not to reveal confidential Cabinet discussions or briefings from the public service as part of their new roles.

Following his resignation at this year's election, Mr Pyne took on a part-time consultancy role with EY. The company says his work would help grow its role in the lucrative defence sector.

Ms Bishop took on a non-executive board role with Palladium, which has taken on a number of contracts to deliver Australian aid projects.

The Prime Minister also revealed on Monday he first heard about Mr Pyne and Ms Bishop's new jobs from media reports.

"Serious and legitimate questions have to be asked about whether Mr Pyne's insider knowledge as a former minister could create an unfair advantage for his new employer," Labor's Kristina Keneally said in the Senate.

"This insider knowledge could taint processes or even raise the prospect of litigation. It's situations like these that ministerial standards are precisely designed to prevent," she said after the advice was tabled.

Former deputy prime minister Barnaby Joyce would not be drawn on whether the jobs passed the pub test, saying: "Well, it passed the investigatory test."

"Obviously I think that people rightly have questions that they want answered," he told reporters in Canberra.

"And I suppose they'll read the recommendations as to how those questions were answered, about how you work for a defence organisation when you were the defence minister.

"I mean, they're the questions that people want to see answered in this investigation."

Dr Parkinson's findings did not put One Nation Leader Pauline Hanson's mind at ease.

"He's saying that all rules have been complied with. Maybe we should look at those rules," she told reporters.

"I have a grave concern about people who have held ministerial positions, dealt with companies that have received a million dollars, if not hundreds of millions of dollars in contracts, and now working for those firms?

"It doesn't look good."

- with AAP