Raids at AWU offices 'leaked to damage Bill Shorten's reputation'

Raids at offices of the Australian Workers' Union were leaked to media in part to damage the reputation of federal Labor leader Bill Shorten, a court has been told.

David de Garis, a former media adviser to Liberal Senator Michaelia Cash, today admitted the impact against Mr Shorten was part of his motivation for giving media a hot tip ahead of raids at AWU headquarters in Melbourne and Sydney in October 2017.

"It would have at least been part of my thinking I'm sure," Mr de Garis said in the Federal Court of the subsequent detrimental impact it would have on Mr Shorten.

Camera crews showed up at the offices before Australian Federal Police in a move that raised questions about the motivation behind the raids.

The AWU is arguing in its case against the Registered Organisations Commission and AFP, that the raids were unlawful.

It's alleged they were politically motivated and instigated by Senator Cash in a bid to hurt the union and Mr Shorten.

Mr de Garis has previously told the trial he was given information about the impending raids by the senator's then-chief of staff, Ben Davies.

He is due to give evidence later this week and is also suing the AWU national secretary and BuzzFeed journalist Alice Workman for defamation in NSW.

AWU legal counsel Herman Borenstein QC said that evidence still to come from Mr Davies and commission executive director Chris Enright could provide a basis for an allegation that the latter acted for a purpose that Senator Cash wanted to achieve.

Senator Cash is due to give evidence on Friday, once federal parliament has finished sitting for the week.