Mr Garrett said the decision to purchase a fleet of nuclear-powered submarines was a huge gamble and should not be allowed to proceed, while speaking at a public forum in Melbourne.

"It's the biggest, it's the most costly and it's the riskiest decision ever taken by any Australian government short of governments committing us to war and should not be allowed," he said on Friday.

He applauded recent backlash from some Labor party members and unions, saying a slew of academic and foreign policy experts also backed the push against AUKUS.

"So we are not alone, a basic and a major objection to AUKUS lies in the aspects of the arrangement which see us reversing our foreign policy and defence posture that's been generally in place since World War II," Mr Garrett said.

"We're going from a focus of direct defence as it is currently constituted to a concentration on forward defence."

Mr Garrett in March said AUKUS would produce increasing volumes of high-level radioactive waste that would be stored for "tens of thousands of years" in the Australian environment.

It follows stinging remarks by former Labor prime minister Paul Keating earlier this year.

Mr Keating said the new security deal was the worst international decision since conscription during WWI.

Under the deal, which is part of the AUKUS security arrangement, Australia will command a fleet of nuclear-powered submarines within the next three decades.

A number of Labor branches have been agitating for the government to dump its support for nuclear-powered submarines and AUKUS.

But Prime Minister Anthony Albanese said his government remains committed.

"The view of my government is very, very clear and is unwavering in its support for AUKUS, in its support for issues about our national security and about our interests in the defence of this nation," he told reporters on Thursday.

"The Labor Party is a democratic party, and it's one in which people engage in debates."

Australian Associated Press