Legal experts, advocates and former refugees have lambasted the Albanese government's migration bill - that could see more than 80,000 people deported - as constitutionally problematic.
The Albanese government has not detailed which countries it has been in discussions with related to a bill that passed the House of Representatives and was examined in a Senate inquiry on Thursday.
The proposed amendments to the Migration Act seek to deport non-citizens, including people not convicted of crimes, and to pay third countries for their part in the removals regime.
Greens senator David Shoebridge pushed Department of Home Affairs officials about which categories of visa holders who were not citizens would be affected.
"Did you inform either or both of the (immigration) ministers (Tony Burke and assistant minister Matt Thistlewaite) that this legislation covers more than 80,000 people?" the senator asked.
"We certainly explained what the definition of a removal pathway non-citizen was ... it's my understanding that ministers have an understanding of the broader cohort," Home Affairs Secretary Stephanie Foster said.
In November, the High Court struck down a case brought by a stateless Eritrean refugee known as YBFZ, ruling it punitive and an overreach, which prompted the government to push the bill before parliament rises for the year.
The proposed amendments would also grant extensive immunity to government officials and those in third countries involved with the removals, and reverse protection findings for refugees.
Witnesses to the hastily called inquiry rejected the bill, with the Human Rights Law Centre bluntly describing it as "constitutionally unsound".
Law Council of Australia President Greg McIntyre said the measures would test the bounds of the separation of powers principle.
"We regard measures targeting a broad category of bridging visa holders many of whom are vulnerable and have not committed offences.. as an approach that is likely to be incompatible with Australia's international obligations and potentially inconsistent with the decision of High Court," he said.
Refugee Council of Australia Policy Director Rebecca Eckard argued the government hadn't been upfront with Australians about the ramifications of the bill.
"This legislation goes beyond what the government has described about it only applying to people with a criminal history," she said.
"The legislation clearly sets out how it could apply to thousands of others, including recognised refugees and people seeking protection, subjecting them to further harm."
The bill is the government's latest attempt to deal with the political fallout from a landmark ruling last year which found indefinite immigration detention was unlawful, triggering the release of some 200 non-citizens with criminal records.
Released immigration detainees, known as the NZYQ cohort, were strapped with ankle monitors and slapped with curfews.
Under questioning from Liberal senator James Paterson, Home Affairs officials also revealed that 10 people had their ankle monitors and curfews reimposed.
Earlier in the hearing, former Manus Island detainee and award-winning Kurdish-Iranian writer Behrouz Boochani pleaded with the senators to vote down the bill.
"I know that most of the senators in Australia, probably many of them have never even met a refugee ... in their lives. You haven't met them but they are people. Try to imagine who they are. They are just human beings."
