Opposition Leader Peter Dutton says there's no way to sugar coat Australia's massive spend on nuclear submarines and the government needs to come clean on any debts or cuts.
Defence Minister Richard Marles has announced the planned acquisition of eight nuclear powered subs with an asking price of $268-$368 billion.
He said an initial four-year, $9b outlay would not impact spending projections in the budget, with the funds reallocated from a cancelled project and defence department money already set aside.
The outlay of any department added up over three decades would come with a hefty price tag attached, he added.
Treasurer Jim Chalmers said the significant cost would deliver "big returns" on national security and the economy.
"This will deepen and broaden our industrial base and it will help create generations of prosperity and opportunities for more people in more parts of our country as well," he said.
Mr Dutton welcomed the purchase of the submarines but hit back at the explanation of how they would be paid for.
"There's a bit of a Magic Pudding episode going on here that somehow the money's going to appear or it's going to be cost neutral," he said.
"There's no way in which you can sugar coat it. There is extra money that needs to be spent.
"We can't allow Labor to cannibalise the defence force to pay for AUKUS, it's not an either or option."
The coalition promised to scrutinise the spend and ensure transparency.
Mr Dutton has flagged the National Disability Insurance Scheme as one area with "difficulties around the sustainability and the cost trajectory".
But Cassandra Goldie from the Australian Council of Social Service warned it would be "unconscionable" to cut any social services.
The Antipoverty Centre questioned how the government could earmark such a large amount for defence while saying it couldn't afford to increase social housing or welfare payments.
"Ordinary people are suffering while politicians throw money away that could be used to help us," spokesperson Jay Coonan said.
Mr Dutton also said the government needed to ensure there was an allocation for an east coast submarine base, which the coalition committed to but wasn't outlined in the AUKUS announcement.
He accused Labor of withholding information on the base until after the upcoming NSW election, saying it was an important piece of the puzzle when he was defence minister.
"They might see that as a saving, so why wouldn't they commit to it when they've committed to WA and to South Australia?" he asked.
"It was also an important part of trying to attract a workforce on the east coast and this was the clear advice from the navy at the time."
Mr Marles urged people to take a deep breath, with decisions about an east coast base not needed for some time.
"We are taking our time here and all of that is a long way into the future," he said.
