The US Supreme Court has again blocked a Texas immigration law that President Joe Biden’s administration has called unconstitutional from taking effect.
SB4 would allow local and state police to arrest those illegally crossing the border from Mexico.
It would be among the toughest immigration measures in any US state.
A record high of at least 6.3 million migrants have been held crossing illegally into the US since Mr Biden took office in 2021.
In Monday’s ruling, the Supreme Court imposed an administrative stay, meaning SB4 cannot be enforced while emergency appeals from the Biden administration and other challengers play out.
Justice Samuel Alito’s brief order suggested the court could take additional action. It is the third time the conservative justice has paused SB4.
SB4 would empower local and state police officers to stop and arrest anyone suspected of having crossed the border illegally, except in schools, healthcare facilities and places of worship.
Punishments would range from misdemeanours to felonies and potential imprisonment, or fines of up to $2,000 (£1,570).
Penalties for illegal re-entry to Texas could go up to 20 years in prison, depending on a person’s immigration and criminal history.
SB4 was signed into law by Texas Governor Greg Abbott in December. It was initially due to come into effect on 5 March, but was repeatedly stopped amid an ongoing lawsuit.
Governor Abbott – a Republican closely linked with former President Donald Trump – has repeatedly argued that SB4 is necessary to reduce migrant crossings, and that the Biden administration has not done enough to secure the border.
The law was challenged in court by the American Civil Liberties Union and the US Department of Justice, which argued that SB4 conflicted with federal authority to maintain security at the US border.
In late February, a federal judge in Texas temporarily blocked the law, saying that it threatened “the fundamental notion that the United States must regulate immigration with one voice”.
But the New Orleans-based 5th US Circuit Court of Appeals paused that ruling, leading the Biden administration to file its emergency request to the nation’s top court.
In an interview with Fox News on Monday before the court ruling was issued, Texas Lt Gov Dan Patrick said the law was necessary because Texas is being “attacked” by migrants.
“By land, by sea, by air. Literally millions coming across the border,” he said. He also referred to the migrants as a “hostile group” and “an organised militia, in essence”.
The Texas House Mexican American Legislative Caucus welcomed Monday’s ruling.
It said “millions of mixed-status Texan families can breathe a sigh of relief”.
Opinion polls show that immigration and the US-Mexico border is a rising concern for American voters ahead of the November 2024 election.
A Gallup poll released in late February found nearly 30% of Americans believe immigration is the most important problem facing the country, significantly higher than government, the economy and inflation.