Asylum seekers wait between the double fence on US soil along the US-Mexico border near Tijuana, Mexico on May 8, 2023, in San Diego. (PHOTO / AP)

WASHINGTON – A US federal judge on Tuesday blocked President Joe Biden's new regulation restricting asylum access at the US-Mexico border, upending a key tenet of his plan to deter migration after COVID-era Title 42 restrictions ended in May.

California-based US District Judge Jon Tigar stayed the order for 14 days, leaving the restrictions in place for now. The Biden administration within hours appealed to the US 9th Circuit Court of Appeals.

Biden, a Democrat, took office in 2021 pledging to reverse many of the hardline policies of former president Donald Trump, a Republican, but has adopted some Trump-like border measures as record numbers of migrants have been caught crossing illegally.

The ruling followed a legal challenge by the American Civil Liberties Union (ACLU) and other groups, who revived a 2018 case brought against similar asylum restrictions implemented by Trump that Tigar previously struck down.

In a 35-page ruling, California-based US District Judge Jon Tigar – an appointee of former president Barack Obama – said US law explicitly states that crossing the border illegally should not be a bar to asylum

Biden's new asylum regulation, which took effect when Title 42 ended on May 11, presumes most migrants are ineligible for asylum if they passed through other nations without seeking protection elsewhere first, or if they failed to use legal pathways for US entry.

The number of migrants caught crossing the border illegally plummeted in recent months after the new regulation went into place. Whether the trend will continue if the new asylum restrictions are blocked remains unclear.

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In a 35-page ruling, Tigar – an appointee of former president Barack Obama – said US law explicitly states that crossing the border illegally should not be a bar to asylum.

Finding refuge in a third country, such as Belize, Mexico or Colombia, is "infeasible" due to limited processing capacity and other factors in those countries, he said. US law only permits limiting migrants' access to asylum if they pass through a country that "actually presents a safe option," he said.

The Biden administration argued that thousands of migrants per month can enter the US from abroad through new programs, such as one for certain migrants with US sponsors. But Tigar said those programs were not open to everyone and such moves were "irrelevant to the availability of asylum."

Migrants start walking north on their way to Mexico City from Tapachula, Chiapas state, Mexico, April 23, 2023. (PHOTO / AP)

The Biden administration has told migrants at the border they can apply for a time to approach a legal crossing via an app called CBP One. The administration opens 1,450 appointments per day to people in central and northern Mexico.

The Biden administration argued that thousands of migrants per month can enter the US from abroad through new programs, such as one for certain migrants with US sponsors. But Tigar said those programs were not open to everyone and such moves were "irrelevant to the availability of asylum"

Tigar said evidence presented in the case "suggests that migrants waiting in Mexico are at serious risk of violence."

Reuters earlier this month found tens of thousands of people, including families with young children, waiting in dangerous Mexican border towns to snag a spot on the app. Humanitarian groups warned of deteriorating sanitary conditions at migrant camps.

"Each day the Biden administration prolongs the fight over its illegal ban, many people fleeing persecution and seeking safe harbor for their families are instead left in grave danger," said Katrina Eiland, the ACLU attorney who argued the case.

READ MORE: Broad asylum curbs at US-Mexico border unveiled

US Homeland Security Secretary Alejandro Mayorkas defended the legality of the Biden asylum regulation, stressing in a statement that it remains in place for now pending an appeal.

"Do not believe the lies of smugglers," Mayorkas said. "Those who fail to use one of the many lawful pathways we have expanded will be presumed ineligible for asylum."