Home Affairs Minister Peter Dutton warns people smugglers will be popping the champagne corks if Labor wins the next election.
Mr Dutton seized on the first parliamentary speech of former trade unionist Ged Kearney, who on Monday pledged to use her position to push for a more humane refugee policy.
"We've watched this movie before," Mr Dutton said.
"Ged Kearney has no answer for what happens when women and children start drowning at sea again."
The minister said the new Labor member for Batman is "more radical than what the Green member for Batman would have been on this topic".
He claimed if Labor won the next federal election, the "unravelling" of coalition border protection policies would mean people smugglers would be back in business.
"The biggest election party will be in some village where people smugglers are toasting prime minister Bill Shorten because it will mean the boats restart," he said.
Ms Kearney's speech attacked "the shameful policy" of indefinite detention on Manus and Nauru.
"Racist dog whistling has demonised and vilified a community that has everything to give to Australia - and the sacrifice of this human potential has been made solely for political gain," she said.
"I doubt we can afford the ongoing cost to our national psyche of subjecting men, women, and children to years of punitive indefinite detention."
Ms Kearney argued claims to asylum should be assessed "within a fair time-limit", but did not reveal how long she thought that should be.
Opposition Leader Bill Shorten last week insisted a future Labor government won't place any time limits on how long asylum seekers can be held on Manus Island and Nauru.
Labor will debate offshore detention at its July national conference, with a draft party platform seeking to "ensure detention is for no longer than 90 days".
But Greens leader Richard Di Natale was skeptical that the opposition would soften on its continued support for boat turn backs.
"We welcome some of those early noises from Ged, but it's very important that she backs it up with her vote in parliament," Senator Di Natale told Sky News.
