Federal Labor has rejected coalition warnings that asylum seekers transferred to Australia for medical treatment will not be able to be sent back to detention on Manus Island and Nauru.
Attorney-General Christian Porter has blamed poor drafting of medical evacuation laws passed last week against the government's will for the loophole.
Labor's immigration spokesman Shayne Neumann said the new laws had not changed the returns system.
"If a person is transferred to Australia for temporary medical treatment, we will return them to Manus or Nauru once doctors advise they have completed medical treatment," he said in a statement.
"This is a desperate distraction from a government trying anything to hide from its scandals and from bowing down to the big banks."
The government is refusing to release its legal advice, instead committing to provide a summary of the solicitor-general's opinion.
Mr Porter said changes to medical evacuation rules had given asylum seekers a one-way ticket to leave offshore processing.
"Our best advice, very sadly at the moment, is that once someone arrives at the request of two doctors we will not be able to send them back," Mr Porter told the Nine Network on Thursday.
The instigator of the original medevac bill, independent MP Kerryn Phelps, said Mr Porter needed to release the advice in full to the parliament so it can consider what to do next.
She noted there were already hundreds of asylum seekers who had been brought to the mainland from offshore detention for treatment and had not returned, under the government's own laws.
"We need to see the unfiltered, unedited advice of the solicitor-general in order to make a judgment about it," she told ABC radio
Under the new regime, two doctors can recommend asylum seekers currently on Manus Island or Nauru be transferred to Australian territory for treatment.
The government intends to send people to the reopened Christmas Island detention centre, off Western Australia, rather than the mainland.
The attorney-general said the government was "scrambling" to find a way to close the loophole but was yet to resolve the issue.
Under the law, the home affairs minister has 72 hours to decide whether or not to agree to a medical transfer.
If the minister rejects the transfer, the decision may be reviewed by a medical panel, which can recommend it goes ahead.
Mr Porter said the minister would have "no discretion" to refuse someone who might have a serious criminal record or be a threat to Australia.
"The reality is that those types of persons, if they were to be transferred pursuant to this Labor law, would have to be placed in a secure facility which is why we've chosen Christmas Island," he said.
Medecins Sans Frontieres doctor Christine Rufener told the ABC that people would not recover from mental health conditions if sent to Christmas Island.
The island's mayor has said the local hospital only has six beds.
Australian Associated Press