Turnbull Government Minister Michaelia Cash has lost a case in the Federal Court to block access to key documents relating to Australian Federal Police raids on the Australian Workers' Union (AWU) offices.
The AWU is trying to have the investigation by the Registered Organisations Commission (ROC) into donations by the union to activist group GetUp thrown out.
Senator Cash has faced staunch criticism after her staffer, David De Garis, tipped off the media that the raids on the AWU's Sydney and Melbourne offices were imminent.
Mr De Garis has since resigned and joined his former boss, the Fair Work Ombudsman (FWO) and Ombudsman media advisor Mark Lee, in trying to block the AWU accessing documents.
Senator Cash asked the ROC to consider investigating the donations.
That investigation led to the AFP raiding the union's offices, concerned the AWU may destroy documents.
Lawyers for the union, Maurice Blackburn, wanted the Minister and the other parties to hand over all correspondence relating to the investigation in a bid to prove its claim that the entire saga was politically motivated.
On Wednesday morning, Federal Court judge Mordecai Bromberg dismissed an attempt to limit what documents the union could access, saying there was a "reasonable basis" for the AWU to demand copies.
He rejected arguments by the Minister that communications made after the ROC started its investigation were irrelevant, after the union said they may give an insight into the reasons behind the investigation.
"The likelihood may well be small but the time period involved is short and the additional burden on the Minister is unlikely to be large," he said in his judgment.
Judge Mordecai did, however, allow the Minister to hold on to some correspondence between her office and the media and AFP.
But he left open the possibility of allowing the union to reapply for those documents once their lawyers had read the first batch, and deemed further inquiries necessary.
Senator Cash and the other parties have until early January to hand over the documents.
