The Home Affairs Minister will be able to ban asylum seekers from coming to Australia for medical treatment on character grounds if Labor can amend proposed new laws.
Labor MPs agreed in a caucus meeting on Monday night to negotiate with the crossbench on giving the minister power to reject a medical transfer after leader Bill Shorten received a security briefing in the morning.
Labor also wants the proposed bill to only apply to people currently in offshore detention - not new arrivals - and set longer time frames for ministers to make decisions.
A bill making it easier for asylum seekers to get medical treatment in Australia passed the Senate in December with Labor's support, but under pressure from the government the party wants to make more changes to it.
The coalition warns that any changes to border protection policies will see refugee boat arrivals start again.
Security agencies have warned the changes could see up to 1000 asylum seekers brought to Australia within weeks.
Labor will also push for transfer decisions "as soon as practicable", rather than within 24 hours, and the laws will only apply to people currently offshore.
But Greens senator Nick McKim says any changes have to help refugees.
"We're not going to vote for something that would either make no difference, or make life worse for refugees," he told Sky News on Monday.
Dozens of doctors descended on Parliament House in Canberra before Labor's meeting, urging MPs to support the original bill.
"People's lives are at stake - the politicking must stop," the Australian Medical Association's Paul Bauert told reporters.
Home Affairs Minister Peter Dutton said the "unnecessary and counterproductive" changes would undermine offshore processing and restart the people smuggling trade.
"There's no sense in being big-hearted - in getting people out of detention, including children on Nauru - only to find that a boat turns up the next day to refill the places with new arrivals," he told Sky News.
More than 4500 doctors have signed the petition in favour of medivac changes. Advocates say 60 asylum seekers are being held offshore are in critical conditions.
Under the original proposed changes, the final decision on medical transfers of asylum seekers in offshore detention would shift from politicians and public servants to two specially appointed treating doctors.
A minister would be required to review cases within 24 hours and, if they reject an evacuation, an independent health panel would scrutinise the decision.
Australian Associated Press