A federal judge struck down a stringent new asylum policy on Tuesday that government officials have called crucial to managing the southern border, dealing a blow to the Biden administration’s strategy that has coincided with a sharp decline in illegal crossings by migrants in recent months.

The rule, which had been in effect since May 12, disqualifies most people from applying for asylum if they have crossed into the United States without either securing an appointment at an official port of entry or proving that they sought legal protection in another country along the way.

Immigrant advocacy groups who sued the administration said that the policy violated U.S. law and heightened migrants’ vulnerability to extortion and violence during protracted waits in Mexican border towns. They also argued that it mimicked a Trump administration rule to restrict asylum that was blocked in 2019 by the same judge, Jon S. Tigar, of the United States District in the Northern District of California.

Judge Tigar stayed the order for 14 days, agreeing to a request by the Biden administration to give it time to appeal. .

The Biden administration introduced the asylum rule in May, when it lifted a public health measure, known as Title 42, under which illegal crossers were swiftly expelled. Since then, the number of migrants apprehended at the southern border has plummeted: In June, fewer than 100,000 people were arrested, the lowest figure since February of 2021.