Key points

Coalition heavyweights defend Senator Cash

Labor calls for resignation after Cash staffer admits he tipped off media to AFP raids

Union attempts FOI to expose communications from inside Cash’s office

The Australian Federal Police should investigate a leak pre-warning media about a police raid on the Australian Workers Union (AWU) that came from the office of employment minister Michaelia Cash, according to the minister herself.

Senator Cash is facing calls from the opposition to resign after it was revealed her media advisor warned some media networks of an impending federal police raid on the AWU’s Melbourne and Sydney offices on Tuesday. News camera crews were in position when police arrived.

The employment minister repeatedly told a Senate Estimates hearing on Wednesday that no one from her office warned anyone in the media.

But later on Wednesday evening, Senator Cash revealed her media advisor had confessed he tipped off journalists around an hour before the raid. The staffer immediately resigned.

"Without my knowledge, one staff member in my office, in the course of discussions with journalists, indicated that he had received information that a raid may take place," she told Senate Estimates on Thursday morning.

"I was not aware of it when I gave those answers yesterday in estimates. All answers that I gave were based on the knowledge that I had at the time."

She said she came back to the Senate hearing to correct the record as soon as she learned "a staff member had unfortunately misled me".

The revelations over the media tip-off come amid accusations from Labor that the AFP were indirectly instructed by the government to raid the AWU. Bill Shorten said the raids were part of a "political witch hunt".

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The raids were in support of an investigation into the AWU by the relatively new Registered Organisations Commission (ROC), which was set up by the government in May to regulate unions and employer groups.

In August, Senator Cash instructed the ROC to investigate the AWU over a $100,000 donation from the union to the activist group GetUp in 2005, when Mr Shorten was the leader of the union.

Senator Cash read the Senate hearing a letter she has written to the head of the ROC, asking him to consider referring the leak to the police.

"One course of action that I would ask you to consider is referring the matter to the Australian Federal Police," the letter reads.

AWU lodges FOI request to determine what Cash knew

The union is lodging a Freedom of Information request to determine whether anyone else in Senator Cash's office knew about the leak to the media ahead of the AFP raid.

The union's national secretary Daniel Walton said the union would not accept one staffer becoming the "fall person" for the leak.

"[Senator Cash] has since thrown a staffer under the bus, but we believe this matter does not sit solely with the staffer," Mr Walton said.

Today we lodged an FOI on Minister Cash’s office. Simple question: what did Cash know and when? What did the PM know and when? #AWUraid — Daniel Walton (@DanWaltonAWU) October 26, 2017

The AWU is also seeking a court order to prevent the seized documents from being used in any ROC investigation, claiming the police warrant was not issued in the proper way.

A Federal Court hearing will be held in Melbourne on Friday.

Cash's colleagues run defence as Labor calls for resignation

The federal opposition is urging the minister herself to resign because she should be held responsible for the actions of her staff.

“Michaelia Cash does have to go,” Labor’s Tony Burke said.

"There needs to be a resignation here because it defies credulity that Senator Cash gave false information five times to the Senate and her staff said nothing."

But senior members of the Turnbull frontbench are defending Senator Cash.

"She is a truthful person," Social Services Minister Christian Porter told the ABC on Thursday morning.

"Clearly here a member of her staff has done something very serious and very seriously wrong, but when Michaelia Cash says that she did not know about that, she is to be believed."

Christopher Pyne, the Minister for Defence Industry, also defended the staffer who admitted to telling the media, David De Garis.

He said he was a "terrific guy" and "great staffer" who had a "lapse of judgement".

The Registered Organisations Commissioner Mark Bielecki fronted Senate Estimates on Wednesday night.

He said the ROC requested the police warrants for the raid in response to information from a “caller”, who warned documents held by the union may be destroyed.