Rachelle Miller, who had an affair with Mr Tudge while working in his office, told of his belittling and humiliating behaviour in a complaint to the Department of Finance.

Mr Tudge learned of the complaint, which was lodged last week, through the media on Tuesday.

"The minister was not aware of any previous complaint," a spokesman told AAP on Wednesday.

"As appropriate, the minister anticipates that the Department of Finance would conduct an independent inquiry into this matter."

Mr Tudge has admitted to the affair.

The explosive complaint, detailed in The Sydney Morning Herald, further fans a political storm over the treatment of women in the federal parliament.

"The strong expectation and culture in parliament was that to be a good staffer you needed to keep quiet, ignore and bury bad behaviour and protect the Liberal Party at all costs," Ms Miller told the department.

"There was no active promotion of a zero-tolerance culture within [ministerial staff]. In fact, I know of some staffers who lodged formal complaints about bullying and were promptly sacked by their ministers.

"Of course we were afraid to speak up. We knew that we were able to be sacked by our minister at any time, so we did not report poor behaviour."

Confirmation of her complaint comes after an ABC Four Corners investigation into the treatment of women by Mr Tudge and cabinet colleague Christian Porter.

Finance Minister Simon Birmingham told parliament on Wednesday, when asked by Labor about the complaint, that there were "well established procedures" for dealing with such allegations.

"They are handled independently of government and in a confidential and thorough way," he said.

"That proper process ought be followed and I have confidence the department of finance will follow it."

Families Minister Anne Ruston played down the revelations.

"I can only speak about my own personal experience with the people concerned and they have always been extraordinarily respectful towards me," she told the ABC.

"And I think, you know, these were issues that happened a long time ago."

Allegations against the two ministers predated changes to the ministerial code of conduct, which banned sexual relations with staff.

Attorney-General Mr Porter has denied accusations of any wrongdoing, saying the 2017 incident canvassed by Four Corners involved nothing more than having a drink with a woman in a bar.

Prime Minister Scott Morrison has refused to take action against either minister involved.

But he has encouraged the opposition to enforce the same standards of behaviour, which veteran Labor MP Joel Fitzgibbon is open to.

"I believe that would be now consistent with the standard the broader public would expect of us," Mr Fitzgibbon told ABC radio.

Labor has its own internal complaints process for staff members, established by former deputy leader Tanya Plibersek.

Mr Morrison has attracted criticism for speaking over Senator Ruston at a news conference on Tuesday when she was asked whether the culture for women in parliament had improved.

"Standing by the men. Speaking over the women. Says it all," tweeted former Liberal MP Julia Banks, who quit the party to become independent after experiencing bullying.

Australian Associated Press