Anthony Albanese will receive advice next week on the legal impacts of Scott Morrison's decision to hold five other ministerial portfolios in government.
The prime minister revealed on Tuesday Mr Morrison had been sworn into the finance, treasury, health, home affairs, and resources and industry portfolios in secret.
An administrative arrangements order signed by Mr Morrison and Governor-General David Hurley on June 28, 2021, also gave Mr Morrison oversight of some social services legislation.
The solicitor-general is due to provide advice on Monday.
"The Westminster system (of government) relies upon checks and balances," Mr Albanese said in Canberra.
"The former government, Scott Morrison and others who were involved in this, deliberately undermined those checks and balances that are so important for our democracy."
Mr Morrison's appointments were made between March 2020 and May 2021.
"The implications are still being worked through. We know there's a legal matter in the issue of resources," Mr Albanese said, referring to the PEP-11 gas project off the NSW coast.
"I'm seeking further advice as to the use of these extraordinary powers by Scott Morrison and other examples of it."
Mr Morrison defended his actions in a 1200-word Facebook post, saying it was a precaution taken during the middle of the pandemic.
"The risk of ministers becoming incapacitated, sick, hospitalised, incapable of doing their work at a critical hour or even fatality was very real," he wrote.
"The home affairs minister was struck down with COVID-19 early in the pandemic and the UK prime minister was on a ventilator and facing the very real prospect of dying of COVID-19.
"As prime minister I considered it necessary to put in place safeguards, redundancies and contingencies to ensure the continuity and effective operation of government."
The prime minister also expressed some remorse over his actions.
"In hindsight these arrangements were unnecessary," he said of the treasury and home affairs portfolios.
"For any offence to my colleagues I apologise."
Mr Morrison says he did not inform most of the ministers about his intervention as he did not want his colleagues second-guessing themselves.
"Ministerial briefs were not copied to me as prime minister in a co-minister capacity. These arrangements were there as a 'break glass in case of emergency' safeguard," he said.
"I also didn't wish ministers to be second-guessing themselves or for there to be the appearance to be a right of appeal or any diminishing of their authority."
Mr Morrison said he took over the resources portfolio to ensure the PEP-11 project was stopped.
"If I wished to be the decision-maker, then I had to take the steps that I took," he told Sydney radio station 2GB.
"I sought to be the decision-maker on that issue because of its importance."
It was the only issue he used his ministerial powers to intervene in, he said.
Former home affairs minister Karen Andrews said Mr Morrison should resign from parliament after "betraying" the Australian people.
Former treasurer Josh Frydenberg told The Australian he was never informed Mr Morrison had himself sworn in to the portfolio.
A representative of Governor-General Hurley says he followed processes consistent with the constitution in appointing Mr Morrison to the additional portfolios.
"It's not uncommon for ministers to be appointed to administer departments other than their portfolio responsibility," the representative said.
But Mr Albanese did not commit to releasing the instruments or changing the process that allowed the signings to be done in secret without being gazetted or otherwise made public.
"I'm open to a change of reforms or suggestions," he said.
"But let's be clear, this isn't business as usual. Conventions apply to the way our democracy functions."
Opposition Leader Peter Dutton said he did not know Mr Morrison had sworn himself into the cabinet positions, but urged calm over calls for a resignation.
"Frankly, it's time for cooler heads to prevail," Mr Dutton told reporters in Tasmania.
"(The prime minister) sees a political advantage. We're better to wait for that legal advice before you make any decisions about what should occur next."
© AAP 2022