Mr Dutton said any new arrivals would go to Nauru, but added it was also possible medical transferees could end up on Christmas Island, where the detention centre will be reopened after closing in October previous year.
The legal advice, which was tabled in Parliament on Tuesday afternoon by the Speaker of the House of Representatives, Tony Smith, raised the stakes by turning the bill into a money bill that could become a test of confidence in the government.
Labor is negotiating with crossbench MPs to change proposed new laws making it easier for asylum seekers in offshore detention to fly to Australia for medical treatment.
If approved, the person will be brought to the detention camp on Christmas Island, which is an Australian territory closer to Indonesia than the mainland, for treatment.
He was also told it could result in 1,000 asylum seekers transferred to Australia within weeks.
Refugee advocates applaud the law that they regard as a more humanitarian approach toward asylum seekers.
"My job now is to ensure the boats don't come", Morrison said.
However, refugee advocates have attacked the current system for being too opaque, with decisions on transfers taking too long, in some cases months, despite people requiring urgent medical attention. "He has led this process to weaken and compromise our borders".
"It should come as no surprise to people that people smugglers have heard what is going on", Mr Dutton said.
The Labor leader said the Coalition should be "ashamed of themselves for luring people to Australia by somehow implying that this Government hasn't got strong borders".
Prime Minister Scott Morrison, who had staunchly opposed the bill, responded by saying the measure could undermine national security, offering a preview of what is likely to be his campaign pitch, and the election's central issue. After he left office, the center-left Labor government began holding refugees on Christmas Island.
"I just say to people trying to put out the welcome mat for people smugglers, the medivac legislation applies for people who are already there, it does not apply to anyone new", he told reporters.
"The one thing that has not changed is the fact that anyone who gets on a boat today, not one thing has changed for them".
Scott Morrison announced $78 million in fresh funding for families escaping domestic abuse, as part of a wider speech about domestic and global security.
The man was arrested after police were called and transferred to Villawood detention centre. As of December, 380 boat people were in detention and 15,674 in the community.
This change is meant to protect refugees who need medical help but might have been convicted of minor offences or perhaps crimes of freedom of expression in their home countries.