Editor's note: This article has been updated to reflect a new hearing date and include statements from the Mexican Ministry of Foreign Affairs and the White House.

Texas police can begin arresting people suspected of illegally crossing the Texas-Mexico border after the U.S. Supreme Court greenlit the state’s controversial immigration law, Senate Bill 4.

Reversing the previous day’s order, the conservative-majority court ruled on March 19 that SB 4 can take effect while the 5th U.S. Circuit Court of Appeals considers if the law is constitutional.

Hours after the ruling, the appeals court announced it would hold a virtual hearing on the case at 10 a.m. March 20. An in-person hearing was originally scheduled for April 3 in New Orleans.

The March 19 ruling is not final, and the case could return to the Supreme Court as the legal battle continues.

What’s happening

The high court denied the Biden administration’s request to block the law. The U.S. Justice Department argued states cannot enforce immigration restrictions, which the federal government historically has had full authority over.

Liberal justices Sonia Sotomayor, Ketanji Brown Jackson and Elena Kagan dissented from the court’s decision.

Passed by Texas lawmakers in November, SB 4 creates state offenses for entering Texas from Mexico outside a port of entry, which is already a federal crime. Undocumented migrants will face up to six months in jail or a $2,000 fine, while repeat offenders could face felony charges.

As the appeals court considers SB 4, state and local police can begin arresting and detaining migrants for illegal entry and re-entry. Judges can prosecute migrants or order them to return to Mexico.

Mexican officials, however, said they would not accept deportations from Texas.

“Mexico reiterates its legitimate right to protect the rights of its nationals in the United States and to determine its own policies regarding entry into its territory,” the Mexican Ministry of Foreign Affairs said in a March 19 news release. “Mexico recognizes the importance of a uniform migration policy and the bilateral efforts with the United States to ensure that migration is safe, orderly and respectful of human rights, and is not affected by state or local legislative decisions. In this regard, Mexico will not accept, under any circumstances, repatriations by the state of Texas.”

Texas is currently the only state with the power to deport migrants. In 2012, the Supreme Court struck down portions of an Arizona law that would have given the state similar authority.

“​​We fundamentally disagree with the Supreme Court’s order allowing Texas’ harmful and unconstitutional law to go into effect,” White House Press Secretary Karine Jean-Pierre said in a statement.” SB 4 will not only make communities in Texas less safe, it will also burden law enforcement, and sow chaos and confusion at our southern border.”

How we got here

SB 4 was originally set to take effect March 5, but was delayed after the Justice Department and immigrant rights groups sued Texas over the measure’s constitutionality.

Gov. Greg Abbott and other top Texas Republicans have argued the law is necessary to curb unauthorized immigration. Abbott frequently criticizes President Joe Biden’s border policies and has asserted that Texas is under an “invasion” by migrants and drug cartels.

In a post on X, formerly Twitter, Abbott said the Supreme Court’s ruling was “clearly a positive development” and noted the upcoming hearing in the 5th U.S. Circuit Court of Appeals, which is scheduled for April 3.

Attorney General Ken Paxton, whose office has defended SB 4 in court, also celebrated the decision on X, calling it a “huge win.”

“Texas has defeated the Biden Administration’s and ACLU’s emergency motions at the Supreme Court,” Paxton wrote. “As always, it’s my honor to defend Texas and its sovereignty, and to lead us to victory in court.”

On Feb. 29, U.S. District Judge David Ezra temporarily blocked SB 4, writing that it was “patently unconstitutional” and would cause “irreparable harm” to the federal government. He pointed to the Supreme Court’s 2012 ruling on the Arizona law.

Texas quickly appealed to the 5th Circuit court, which said the law would take effect March 10. The appellate court did not explain its decision.

Supreme Court Justice Samuel Alito extended pauses on the law three times before the March 19 ruling.

What they’re saying

The Supreme Court did not remark on whether SB 4 is constitutional. In an opinion concurring with the six-member majority’s ruling, Justice Amy Coney Barrett wrote the case was in a “very unusual procedural posture.”

Noting that the 5th Circuit has not made a formal decision on the law, Barrett wrote that “before this Court intervenes on the emergency docket, the Fifth Circuit should be the first mover. ... It can presumably do so promptly.”

“If a decision does not issue soon, the applicants may return to this Court,” she concluded.

In a dissenting opinion, Sotomayor slammed the conservative justices for allowing SB 4 to take effect.

“The Court gives a green light to a law that will upend the longstanding federal-state balance of power and sow chaos, when the only court to consider the law concluded that it is likely unconstitutional,” Sotomayor wrote.

Texas immigrant rights groups and their lawyers called the ruling “disappointing” and “a setback” in statements March 19.

“Allowing this law to be implemented as the case makes its way through the legal process needlessly puts people’s lives at risk,” said Tami Goodlette, a lawyer with the Texas Civil Rights Project. “Everyone, no matter if you have called Texas home for decades or just got here yesterday, deserves to feel safe and have the basic right of due process. We remain committed to the fight to permanently overturn SB 4 to show the nation that no state has the power to overtake federal immigration authority.”