The nation's construction union will submit CCTV footage to support its claims police breached procedural rules during a raid of the ACT headquarters.
The Construction, Forestry, Mining and Energy Union has argued union officials were not given their "right to observe" and not told what files were being taken during the 13-hour raid of the Dickson office on August 25.
They attempted to file an affidavit of a union official on Monday morning which included stills from the footage.
About 20 police, acting on evidence gathered through the Royal Commission into Trade Union Governance and Corruption, raided the Dickson office about 10.45am on August 25 and seized about 10,000 electronic and hard copy files.
The police have subsequently volunteered to not access or examine seized materials – effectively halting part of the probe – until a court can rule on the lawfulness of the search and confiscation.
Union barrister Peter Morrissey, SC, told the ACT Supreme Court on Monday the police moved union officials out of the secure office area into the reception area as soon as they arrived, and only explained the search warrant – one of two executed on the day – after the search had begun.
Mr Morrissey said the union would use the CCTV footage to back its claim the office area, which was guarded by a police officer, was a "no-go zone" for its officials during the search which involved police copying the "entire server".
After an initial objection from the federal police on the grounds of lack of notice, the affidavit was accepted by the court.
Mr Morrissey said the police disputed the argument the search began before the first warrant was explained to three officials.
He said the union had no opportunity to use their "right to observe" until a solicitor for the union arrived at 11.52am, after which the solicitor was given a "partial ability" to observe the seizures.
Mr Morrissey said before the first warrant's 9pm deadline a second search warrant was issued, with police leaving the site then re-entering at 9.02pm.
"The failure to provide a property seizure record is not a mere glitch, but is the loss of a substantive right," he said.
Barrister for the police Andrew Berger said police would need time to view the "12 to 15 hours" of footage and present additional material to the court. The matter was adjourned for a two-day hearing beginning on October 19, when parts of the video footage are expected to be shown. The union was ordered to pay the police costs for the day.