By Andrew Chung

WASHINGTON (Reuters) -U.S. Supreme Court justices on Tuesday grappled with President Joe Biden’s bid to rescind a hardline immigration policy begun under his predecessor Donald Trump that forced tens of thousands of migrants to stay in Mexico to await U.S. hearings on their asylum claims.

The justices heard oral arguments in a Biden administration appeal of a lower court ruling reinstating Trump’s “remain in Mexico” policy after the Republican-led states of Texas and Missouri sued to maintain the program. Biden suspended Trump’s policy, which had changed longstanding U.S. practice, in January 2021 shortly after taking office and acted to rescind it five months later.

Some of the conservative justices, who hold a 6-3 majority on the court, questioned the extent of the administration’s discretion to release migrants into the United States, but also Texas’s use of the courts to constrain the U.S. government in an area over which typically there is broad federal authority.

“There’s no real explanation of how the public is benefited by more people coming into the United States who are not lawfully admitted into the United States rather than trying, if feasible, for some of those people to remain in Mexico,” conservative Justice Brett Kavanaugh said.

Conservative Chief Justice John Roberts questioned the Biden administration’s view of the law.

“There is no limit, as you read the statute, to the number of people that you can release into the United States, right?” Roberts asked Solicitor General Elizabeth Prelogar, arguing for Biden’s administration.

Roberts also told Texas Solicitor General Judd Stone that it seemed a “bit much” for Texas to “substitute itself” for the federal government to determine the best way to comply with U.S. immigration law.

Trump’s administration adopted the policy, formally known as the “Migrant Protection Protocols,” in response to an increase in migration along the U.S.-Mexican border in 2018. The policy prevented certain non-Mexican migrants, including asylum seekers fearing persecution in their home countries, from being released into the United States to await immigration proceedings, instead returning them to Mexico.

Biden’s fellow Democrats and immigration advocates criticized the policy, saying migrants stuck in Mexican border cities have faced kidnappings and other dangers.

At issue in the case is the meaning of a provision of a 1996 U.S. immigration law that says U.S. officials “may return” certain immigrants to Mexican territory pending immigration proceedings. Texas and Missouri have said this provision must be used because the United States lacks detention space for migrants.

Prelogar called the provision discretionary and said the lower court’s decision means that “every presidential administration, in an unbroken line for the past quarter century, has been in open violation” of the law. Administrations prior to Trump’s presidency had used the provision sparingly.

For migrants not posing a security risk, immigration law separately allows their release into the United States for humanitarian reasons or “significant public benefit” pending a hearing, a practice officials have followed for decades.

The administration said lower courts are unacceptably interfering with the historically broad authority that U.S. presidents have held over immigration and foreign affairs.

Liberal Justice Elena Kagan said because the United States needs Mexico’s consent to send migrants there, the Texas challenge “to basically tell the executive how to implement its foreign and immigration policy … puts the United States essentially at the mercy of Mexico.”

Roughly 68,000 people fell under the “remain in Mexico” policy from the time it took effect in 2019 until Biden suspended it.

The number of migrants caught crossing the U.S.-Mexico border has reached record highs recently. Republicans have criticized Biden’s immigration policies and contend that the “remain in Mexico” policy effectively deterred unlawful migration.

After a judge ruled in favor of Texas and Missouri, reinstating the program, the Supreme Court last August refused the administration’s request to block that decision while it appealed.

The New Orleans-based 5th U.S. Circuit Court of Appeals ruled in December that because the government lacks the capacity to detain all migrants eligible for admission pending a hearing, it must maintain “remain in Mexico.”

(Reporting by Andrew Chung; Editing by Will Dunham)

---