A media advisor working for the Registered Organisations Commission (ROC) — who had been offered a job in Senator Michaelia Cash's office — was the source of a leak about federal police raids on offices of the Australian Workers' Union in 2017, the Federal Court has heard.

Key points: The AWU is seeking to shut down a ROC investigation into donations it made to GetUp! in 2006

The AWU is seeking to shut down a ROC investigation into donations it made to GetUp! in 2006 As part of the ROC investigation, the AFP raided the union's Sydney and Melbourne offices in October 2017

As part of the ROC investigation, the AFP raided the union's Sydney and Melbourne offices in October 2017 Senator Cash's former chief of staff Ben Davies named Mr Lee in a police statement as the source of a leak about the raids

Mark Lee was on secondment to the newly established ROC in October 2017 when 32 Australian Federal Police officers swooped on the union's offices in Melbourne and Sydney.

The AWU is challenging the validity of the ROC investigation into AWU donations to the activist group GetUp! in 2006, when Opposition Leader Bill Shorten headed the union.

On day four of the civil trial, the court heard Mr Lee had been named in a police statement given by another witness, Ben Davies, who was Senator Cash's chief of staff when the raids took place.

The court heard on Monday that it was Mr Davies who passed on the information to Minister Cash's senior media advisor, David De Garis.

Senator Cash's then-media advisor, David De Garis, tipped off print journalists about the raids. ( ABC News: Karen Percy )

Mr De Garis then made contact with newspaper journalists to advise them of the raids.

He was assisted by Michael Tetlow, who was working for the then justice minister, Michael Keeenan.

Mr De Garis's evidence directly contradicts Mr Keenan, who maintains his office was not involved in tipping off journalists to the raids.

Sorry, this video has expired Michael Keenan faces questions in Parliament over media leaks

Mr Davies told the court he had assisted Senator Cash in drafting letters to the ROC, which were sent on August 15 and August 17, 2017.

He also told the court he oversaw policy development, media coverage and other issues and consulted with other staff, including Senator Cash.

"The consultation was in the context of media coverage and the minister's position that she ought to adopt," Mr Davies said of his role.

The Australian newspaper had published a number of articles about the GetUp! donations at that time.

The AWU is arguing the ROC investigation was politically motivated.

Federal police raided the AWU's offices on October 24, 2017. ( AAP: Julian Smith )

Its lawyer, Herman Borenstein SC, asked Mr Davies about his contact with Chris Enright, a senior officer at the ROC.

The court heard the men had met only once in July 2017 in "an informal meet-and-greet" just after the ROC was established.

The men had spoken a number of times, including after the second letter of referral was sent to the ROC.

"He indicated that the letter had been brought to his attention and he asked for it to be re-sent," Mr Davies said.

Michael Tetlow told TV networks the AFP was about to raid the union's offices. ( ABC News: Michael Tetlow )

The court heard Mr Davies also worked in the office of former Victorian Attorney-General Robert Clark in 2011.

He is currently a policy consultant in Canberra.

Mr Davies will continue his evidence next week.

On Friday, Senator Cash is expected in the witness stand.

Mr Lee is also slated to give evidence in the trial.