Liberal MP James Newbury used the legal immunity on Monday to identify Ringwood MP Dustin Halse as the state government member who allegedly had sex in their parliamentary office in December 2020.

The allegation was first reported by the Herald Sun in May, though they did not name Mr Halse.

There is no suggestion in the report that the backbencher was engaged in criminal behaviour or that the sex was non-consensual.

"The Speaker's confirmed an investigation into the member for Ringwood bonking in his office," Mr Newbury told the Public Accounts and Estimates Account Committee hearing on Monday while holding up the Herald Sun report.

His line of questioning was quickly shut down by state government MPs, who form a majority on the committee.

Acting Premier James Merlino said the government raised concerns about Mr Halse's conduct with the Speaker of the Legislative Assembly Colin Brooks in May.

"As I've said before, the behaviour was completely inappropriate and falls short of community expectations," he told reporters on Tuesday.

Mr Merlino said he had spoken privately with Mr Halse and expressed his views on the matter.

But he added any further action or sanctions would need to be imposed by Mr Brooks.

"It's not action that I would take," Mr Merlino said.

The acting premier conceded there was a "broader issue around culture and behaviour" within parliament, which has also been subject to a review by Mr Brooks and his counterpart in the Legislative Council, Nazih Elasmar.

Their report, which proposes a revamp of the laws governing politicians' behaviour in the workplace, is currently with the state government.

"No workplace is immune and the parliament is no different to anywhere else, and we expect appropriate behaviour in our workplace," Mr Merlino said.

A spokesman for Mr Brooks said no investigation had been or was being undertaken into the matter.

Opposition Leader Michael O'Brien described the alleged behaviour as clearly inappropriate.

"What people do in private is a matter for them, but there's a time and a place and parliament is not the place," he told reporters outside parliament.

"We're sent here to work for Victorians, we're sent here to serve the public, not to look after ourselves."

Mr O'Brien said Mr Halse "at the very least" should publicly apologise, though sanctions should also be considered by the state government.

Reason Party MP Fiona Patten said Mr Newbury had "dropped to a new low" by naming Mr Halse.

"I feel that other women in this place who have experienced sexual harassment are going to find it difficult to come forward because they're worried it will go straight out into the public arena," she said.

When asked if it was appropriate for MPs to have sex in their office, Ms Patten replied: "When I was first elected here, my partner and I were pretty happy, pretty excited, we may have got a little bit amorous."

Mr Halse was elected in November 2018, reclaiming the seat of Ringwood from the Liberals in Labor's landslide state election win, and currently sits on the Integrity and Oversight Committee.

He has been contacted for comment.

Australian Associated Press