Senator Michaelia Cash has revealed a “media source” within the Registered Organisations Commission (ROC) tipped off her office that raids on union offices would or may happen.

But the cabinet minister told a Federal Court hearing on Friday the first she knew of October 2017 federal police searches of Australian Workers’ Union offices in Melbourne and Sydney was seeing them on the television news.

Three people tied to her office have been named as sources of tip-offs to the media of the raids, as part of an investigation by the Registered Organisations Commission into union donations.

The union is taking action against ROC, claiming an investigation into the AWU was a political play to harm the profile of Labor leader and former union secretary Bill Shorten and the raids were therefore unlawful.

Senator Cash said she believes her office was notified in advance of the raids by the commission, because its operation fell within her portfolio as then employment minister.

She first became aware of the investigation the day before, she said.

That was eight weeks after she wrote to the commission to make them aware of allegations she’d seen in an August 2017 media report that the union may have broken its rules by failing to get authorisation for a $100,000 donation to activist organisation GetUp in 2006, when Mr Shorten was on its board.

She wrote again, raising a $25,000 donation to Mr Shorten’s election campaign from the AWU.

Senator Cash said she knew she couldn’t direct the independent ROC to investigate, but felt it was incumbent upon her to ensure the watchdog was aware of potential wrongdoing.

“It wasn’t for me to be pleased or not,” Senator Cash said, of her reaction to news an investigation was underway.

A number of people were outed in the hearings as having prior knowledge of the raids, including Mark Lee who was a media adviser on secondment to the commission and who had been offered a job as the Senator’s media adviser.

He was said to have passed on details to Senator Cash’s then chief of staff Ben Davies, who passed on the information to her media adviser David de Garis, who conspired with former Justice Minister Michael Keenan’s then media adviser Michael Tetlow to contact journalists.

Mr Lee didn’t take up the job in Senator Cash’s office and Mr Davies, Mr de Garis and Mr Tetlow have all since changed jobs.

Senator Cash was also quizzed by the union’s legal counsel Caryn van Proctor about her contact with ROC executive director Chris Enright, who is also due to be called as a witness.

She said she couldn’t recall any contact beyond pleasantries during senate estimates.

But she also revealed she’d become aware, during document discovery for this case, of a file note recording contact between Mr Enright and Mr Davies in August 2017.

-AAP