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

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

Immigrant advocacy groups that sued the administration said the policy violated US law and increased immigrants’ vulnerability to extortion and violence during long waits in Mexican border cities. 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 from the Biden administration to give him 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 quickly removed. Since then, the number of migrants apprehended at the southern border has plummeted: Fewer than 100,000 people were apprehended in June, the lowest number since February 2021.