The Australian Federal Police has been ordered to pay the bulk of the construction union's costs for the court challenge against an illegal raid on its Canberra headquarters.
Police seized thousands of documents from the CFMEU's Dickson offices in search of evidence of blackmail and corruption during the high-profile raids, triggered by evidence given to the trade unions royal commission in August 2015.
About 20 police attached to the royal commission were believed to have taken electronic and hard copy files, as well as mobile phones, as they frisk-searched union officials and staff, removed posters, and sifted through the office safe and ceiling cavity.
They stayed at the headquarters for about 13 hours.
The union launched legal action against the AFP in the ACT Supreme Court, claiming the confiscation of the documents was unlawful on numerous grounds and there was no evidence to support the issuing of a second warrant.
Justice Richard Refshauge later upheld the majority of the union's challenges and found part of the search of the Dickson offices had been unlawful.
He ruled that police withheld information from the magistrate in order to get the warrant.
"I have found the seizure under the second warrant to be invalid because of the failure to disclose fully the circumstances that were required to be disclosed for the issuing officer, the learned magistrate, to make a proper decision about whether to issue a warrant that is able to be executed after 9pm," the decision said.
"In the light of the strict duty of full disclosure, it seems to me that this failure meant that the warrant was issued on a false basis and is therefore invalid."
The judge ordered information seized – which the union says was electronic data – under the second warrant should be destroyed or returned to the union with seven days.
He also ordered the AFP pay the union's legal costs for the challenge, but that order was later disputed by the AFP.
The matter returned to the Supreme Court on Thursday, when Justice Refshauge said the AFP should pay 85 per cent of the union's costs for proceedings.
Justice Refshauge said in his decision he moderated the costs order to reflect the fact the court had upheld some of the challenges made by the AFP.