Senator Nick Xenophon has called for an independent inquiry into the source of a media tip-off ahead of federal police raids on Bill Shorten’s former union.

The AFP raided Australian Workers Union offices in Sydney and Melbourne on Tuesday in full view of a waiting media pack.

“The public deserve to know how and why the media were tipped off about these raids. The tip-off compromises the integrity of the entire process,” he said.

“The rule of law is being turned into a farcical sideshow with tip-offs like this. It drags the AFP and ROC into a highly partisan and toxic environment.”

Labor backed Mr Xenophon’s call in a statement from Shadow Minister for Employment and Workplace Relations Brendan O’Connor.

The raids were part of an investigation by union watchdog, the Registered Organisations Commission (ROC), into donations made when Mr Shorten was head of the AWU.

Mr Xenophon, whose vote was critical to the creation of union watchdog ROC, said the Commission’s credibility and integrity was at stake as a result of the media tip-off.

The ROC on Tuesday said it sought warrants to the offices because it was concerned documents relevant to the investigation were being tampered with. It is a claim unions have denied.

During Parliament Question Time on Wednesday, Manager of Opposition Business Tony Burke asked Mr Turnbull twice if he could guarantee if Employment Minister Michaelia Cash or her office had tipped off the media about the raids.

Mr Turnbull deflected the question at first, before saying that Senator Cash “has assured me she did not advise any journalists about the raid”.

He did not comment on whether any of the Senator’s staff may have contacted the media.

Asked by Labor senator Doug Cameron whether anyone in her office had given advance notice to media about the raids, Employment Minister Senator Cash said she was “certain” no one in her office had contacted media.

Ms Cash said she found out about the raids “as they unfolded on television” and her office only learned of them when they commenced.

On Wednesday, Maurice Blackburn lawyers representing the AWU filed an application seeking an urgent hearing in the Federal Court to determine the validity of the raids.

The hearing was adjourned until Friday and the ROC agreed not to receive any documents from the AFP until then.

The ROC is investigating donations made to GetUp Limited during the financial year ending 2006, plus donations to a range of recipients during the financial year ending June 30, 2008.

These include a $25,000 payment to Mr Shorten’s 2007 election campaign in the Melbourne seat of Maribyrnong and another two payments to Labor campaigns in the seats of Petrie (Queensland) and Stirling (WA).

-with AAP