Ministers must be held accountable for any role they played in one of the biggest security breaches in Australian history, Opposition Leader Bill Shorten has said.
Mr Shorten has written to Prime Minister Malcolm Turnbull urging him to review and strengthen the storage and protection of highly classified information in light of The Cabinet Files.
Hundreds of classified documents obtained by the ABC have been returned to the Government after it was revealed they were found in two filing cabinets, sold at an ex-government sale.
Mr Turnbull said the security breach was "shocking" and called for the public servants responsible for the breach to be sacked.
The Department of Prime Minister and Cabinet (PM&C) confessed it lost the documents and its secretary, Martin Parkinson, said the beach cast his workforce "in a poor light".
The Australian Federal Police has launched an investigation into one of the biggest security breaches in Australian history, but Mr Shorten said it must not solely focus on the Australian Public Service.
"The end result cannot be simply to slate blame to a middle-ranking or departmental officer deemed to be expendable," he said.
"Accountable senior departmental staff and the relevant ministers need to be held to account where shortcomings are identified.
"Procedures must be comprehensively overhauled to address the serious deficiencies that led to this event."
The Cabinet Files revealed documents were left in Penny Wong's office when Labor lost the 2013 election, although the files were locked down in a safe.
Westminster convention stipulates cabinet ministers bear the ultimate responsibility for the actions of their staff.
Cabinet ministers have been busy assuring Australia's security partners that the Government can protect highly classified information.
Mr Shorten said he appreciated a briefing from PM&C on the security breach and said he would continue to monitor the investigation.
"I appreciate that you have publicly stated in strong terms your concern over this breakdown in security procedures that occurred after the Coalition was elected, and have highlighted your intention that the incident is investigated and those responsible held to account," Mr Shorten said.
"As current custodians of Australia's national security interests, however, it is incumbent on you and your Government to also thoroughly explore security procedures to not only discover how this extraordinary error has occurred, but to ensure that it cannot happen again.
"Whether poor Cabinet procedures or bureaucratic incompetence is the cause, I urge you to ensure procedures for the handling and storage of sensitive information by the Government are systematically reviewed and strengthened."