The woman alleges the former Liberal Party staffer reached under the table to stroke her thigh at a Canberra bar in 2017.

She has filed a report at a police station in Canberra and will make a formal statement later this week.

The woman came forward to the ABC after Brittany Higgins alleged she was raped by the man in 2019.

Two other women - a Liberal staffer, and a former party volunteer - have also alleged they were sexually assaulted by him.

Ms Higgins was employed by Defence Minister Linda Reynolds at the time of the alleged assault.

Labor's upper house leader Penny Wong said Senator Reynolds had questions to answer about how the complaint by Ms Higgins was handled.

"She wasn't being treated as a human being. She wasn't being treated as a rape survivor and she wasn't being treated as a victim of a grave crime," she told parliament.

"She was being treated as a political problem."

Senator Wong said Prime Minister Scott Morrison's words rung hollow while there was no culture of accountability.

"We know that at best, Mr Morrison runs a government where the culture is don't ask, don't tell when it comes to serious criminal allegation," she said.

"At worst, Mr Morrison himself is part of the cover-up."

Labor, the Greens and One Nation have accused the government of setting up whitewash inquiries in response to the allegations.

The alleged rape has sparked several inquiries into workplace culture in federal politics.

The prime minister has also endorsed an external complaints handling process for parliamentarians and their staff.

The Greens are calling on the government to set up an independent review into how Ms Higgins' allegations were handled.

Ms Higgins initially chose not to pursue a police complaint, fearing her job would be on the line.

Cabinet Minister Simon Birmingham said in circumstances where somebody chose not to proceed with a police complaint, there was a balance to be struck by those who were informed of the allegations.

He said respecting the rights of individuals to make decisions needed to be weighed against the responsibility of others to pursue action.

Labor MP Joel Fitzgibbon said the cultural problem was one for men - not women - to fix.

"Men have to understand that if they do these things the full force of the law will come down upon them," he told the Seven Network.

Independent MP Zali Steggall has been contacted by former staffers with traumatic stories about their time in parliament.

She wants independent investigations to accept anonymous reports.

"It is very important to come forward with your stories to make sure we draw a line in the sand and this place does not have these incidents and the perpetrators are brought to justice," Ms Steggall told reporters.

"That is the part that I'm most offended about, that we have alleged very serious crimes that have been committed that have not been properly investigated."

Australian Associated Press