Québec Immigration Minister Christine Fréchette described the development as “surprising.” She said it highlighted the need to “solve the problem of Roxham Road,” referring to an unofficial border crossing south of Montreal used by thousands of asylum seekers every year.

Back in 2002, the United States and Canada signed the Safe Third Country Agreement. The treaty requires migrants to make an asylum claim in the first country they enter, whether that be the U.S. or Canada.

“The agreement helps both governments better manage access to the refugee system in each country for people crossing the Canada–U.S. land border,” the Canadian government writes about the treaty. However, the government added the agreement only applies to migrants who arrive:

• at official Canada-U.S. land border crossings
• by train
• at airports, only if the person seeking refugee protection in Canada has been refused refugee status in the U.S. and is in transit through Canada after being deported from the U.S.

This means unofficial border crossings, like Roxham Road, are not a part of the treaty. Fréchette said U.S. and Canadian officials were negotiating to update the Safe Third Country Agreement to include situations like the New York migrants heading to Canada.

“I think it makes the urgency of the situation even more apparent,” Frechétte said.

BBC News contributed to this report.