The Australian Federal Police has launched an investigation into the leaking of information about the raids on the Australian Workers Union headquarters this week.

The office of Employment Minister Michaelia​ Cash, still weathering a political storm over the involvement of one of her staff members in tipping off the media about the raids, has been notified of the leak investigation.

Attorney-General George Brandis said the government and representatives of the Registered Organisations Commission would no longer answer questions on the matter while the police probe is underway.

Senator Cash's senior media adviser David De Garis quit on Wednesday, after admitting he had tipped off members of the media that the raid was imminent – allowing them to be in place when the federal police arrived at AWU offices.