The federal government is trying to block Bernard Collaery and his lawyers from reading a briefing prepared for the prime minister on the East Timor bugging scandal, arguing the material is "cabinet-in-confidence".
Anna Mitchelmore SC, appearing for Attorney-General Christian Porter, argued in the ACT Supreme Court on Wednesday that disclosing this and other documents would have "a particularly chilling effect" on future cabinet deliberations.
But Mr Collaery's barrister, Christopher Ward SC, claimed the material was "a long way removed" from those high-level discussions and should be handed over.
Mr Collaery, a lawyer and former ACT attorney-general, is awaiting trial after pleading not guilty to five charges alleging he breached national security laws and conspired with former spy Witness K to do so.
He is accused of sharing protected information about an operation in which Australian spies bugged a government building in East Timor during negotiations over oil and gas reserves.
Pre-trial proceedings on Wednesday focused on efforts made by Mr Collaery's legal team to access five briefings to senior government figures, including one prepared for the prime minister in the lead-up to a National Security Committee of Cabinet meeting.
The federal government argues it is not in the public interest to provide them, and that doing so would breach cabinet confidence.
Mr Ward said Mr Collaery was not asking for documents that divulged deliberations of cabinet, and the material sought was relevant to his defence.
He acknowledged, however, that it would be difficult to convince the court of that.
"In the absence of seeing the documents ... it is difficult to make submissions relating to the documents themselves," Mr Ward said.
While some of Wednesday's proceedings took place in open court, parts were also held behind closed doors.
Justice David Mossop reserved his decision on access to the documents.
An earlier ruling by the same judge that parts of Mr Collaery's trial will be held in secret - for national security reasons - remains under appeal.