Bill Shorten has slammed Turnbull government plans to end income support for up to 100 Australian-based asylum seekers and give them just three weeks to find a home, describing the decision as the Prime Minister's "weakest move yet".
The Greens have also criticised the move, vowing to try and use parliament to stop the change.
But a spokesman for Immigration Minister Peter Dutton said on Sunday every illegal maritime arrival transferred to Australia for temporary medical assistance was aware that once their medical needs were met they would return to Nauru or Manus.
Human Services Minister Alan Tudge??? also defended the government, declaring the asylum seekers won't receive any further taxpayer support and will have to return to Nauru, Manus Island or their own country.
Fairfax Media revealed on Sunday leaked government documents that showed the Immigration Department will issue dozens of asylum seekers, who were transferred to Australia from offshore detention for medical reasons, with a new visa known as the "final departure Bridging E Visa".
Under the new visa conditions, income support of about $200 a fortnight will cease on Monday and a three-week deadline to move out of government-supported accommodation will be imposed.
In a strongly worded rebuke that will delight asylum seeker advocates and ALP members who have demanded the opposition adopt a more compassionate approach to the issue, Mr Shorten said the decision was a "new low" from the government.
Despite the objections of the left of the ALP, Mr Shorten steered through a seismic policy shift at the 2015 Labor Party conference which saw the opposition commit to turning back asylum seeker boats if it wins government. Under Kevin Rudd, Labor had re-opened offshore processing.
But Mr Shorten said on Sunday that kicking people onto the streets with no support is needlessly cruel and "really dumb".
"It won't fix anything. It's just hurting vulnerable and sick people for the sake of it," he said.
"These people should be eligible for settlement in the United States or other countries in our region - so they have a permanent home. This act has nothing to do with strong borders or stopping people smugglers. It's a weak Prime Minister trying to look tough. That's it.
"Malcolm, this is not strong. This is cowardly and cruel. It's your weakest move yet."
Greens leader Richard Di Natale said on Sunday the party was seeking advice on whether the use of a new 'final departure Bridging E Visa' could be overturned when the Senate returns in a week's time.
"We do call on members of the crossbench and the Labor Party to support us in doing everything we can to stop this unspeakable cruel act getting through the Senate," he said.
In total, there are about 400 asylum seekers and their children living in Australia after medical transfers from offshore processing and, eventually, all of them may be subject to the tough new visa rules. The asylum seekers will be able to work until they leave the country.
Labor immigration spokesman Shayne Neumann had earlier described the decision by the Turnbull government was "even more proof of Peter Dutton's incompetence in the management of offshore processing centres and his failure to negotiate other third country resettlement options".
The Turnbull government and the Obama administration struck a deal for the US to consider taking up to 1250 asylum seekers from Manus Island and Nauru.
While President Donald Trump has lashed the "dumb deal", he has not walked away from it - as a leaked transcript of Mr Trump and Malcolm Turnbull's first phone call revealed - but so far, no asylum seekers have been sent to the US, either, as vetting of the applicants continues.
Labor defence spokesman Richard Marles???, a former immigration minister, said "Australia has an obligation to provide care" to asylum seekers in this country, or on Manus or Nauru, but that "it's very important that Australia remains off the table" as a destination for would-be asylum seekers.
Mr Tudge said the asylum seekers facing the tough new visa conditions had received medical treatment in Australia "and consequently now they are required to go back to Nauru, or to PNG, or indeed back to their home country".
"That is what this is about, and it is consistent ... with the principle that anybody who arrives by boat to our shores, won't be settled in Australia; they will be settled elsewhere. That is what this is about," he told the ABC.
"I cannot confirm the precise number; but it is right that now that they have had their medical treatment in Australia, that they will be required to return to Nauru, to Papua New Guinea, or back to their home country. And there won't be the further provision of taxpayer support in Australia."
The Manus Island processing centre is set to be shut down by October 31.