"Our people, having looked at the bill, believe that in a matter of weeks everybody off Nauru and Manus, essentially regardless of their medical condition, would be in Australia. If you do that, the boats restart."

"Bill Shorten now has advice, he's had briefings. The agencies have told him that this bill would be a disaster, that it would restart boats."

Mr Dutton did not say exactly who had briefed Mr Shorten, but said the advice came through the Australian Security Intelligence Organisation, along with Australian Defence Force chief Angus Campbell and Solicitor-General Stephen Donaghue.

Later, at a press conference, Mr Dutton said it was only his "understanding" that Mr Shorten had been briefed, but acknowledged that such a meeting may not have actually occurred.

"If Mr Shorten is saying he didn't make the meeting, then he should explain why," he said.

A spokesman for Shayne Neumann, Labor's immigration spokesman, said: "Peter Dutton is lying when he claims Labor has received an intelligence briefing on the Phelps bill."

Excerpts of "leaked" ASIO advice appeared in News Corp's The Australian newspaper on Thursday.

The supposed briefings relate to a series of amendments put by independent MP and doctor Kerryn Phelps, which have become a crucial test for the stability of the minority Morrison government.

Labor and the crossbench are on the cusp of having enough votes to pass the legislation against the will of the government. It would be the first time since 1929 that a government has lost a vote on substantive legislation on the floor of the House of Representatives. In 1929, then prime minister Stanley Bruce called an immediate election.

Prime Minister Scott Morrison on Tuesday ruled out calling a snap election if his government lost the vote.

Dr Phelps' legislation would compel ministers to transfer refugees from Manus Island and Nauru to Australia on the advice of two independent doctors in Australia. The minister would have limited capacity to overrule the doctors on security grounds.

Mr Dutton argued the bill would undermine a "central pillar" of Operation Sovereign Borders, and dismissed legal advice obtained by Labor suggesting the bill is written broadly enough to give the minister sufficient power to block transfers to protect border integrity.

"I would have thought Mr Shorten would be best advised to take the advice from the director-general of ASIO, from the chief of the defence force, from the head of Operation Sovereign Borders, from the Australian government solicitor in relation to this bill," Mr Dutton told 2GB.

He dismissed Labor's legal advice as coming from a "suburban lawyer" and "Labor activist".

The government has signalled it would use Labor's support for the bill to hound the opposition on border protection through to the election.

On Tuesday, the Prime Minister claimed the bill risked allowing paedophiles, murderers and other criminals to come to Australia, and would force the government to reopen detention centres including the closed Christmas Island facility.

"This is a stupid bill," Mr Morrison said. "It's written by people who haven't got the faintest idea how this works."

On Thursday, Dr Phelps retweeted a tweet from veteran press gallery journalist Michelle Grattan accusing the government of "making very political use of ASIO", which was "what was feared when put under Home Affairs" - the super-department headed by Mr Dutton since late 2017.