A federal appeals court has again blocked a law that makes it a state crime for migrants to illegally cross the border into Texas, hours after the U.S. Supreme Court’s conservative majority allowed the law to take effect while challenges to it continue through the court system.

The U.S. Court of Appeals for the 5th Circuit blocked enforcement of the law, known as S.B. 4, ahead of oral arguments scheduled for Wednesday morning.

Two justices in the Supreme Court majority had said the high court may again consider intervening after the 5th Circuit weighs the merits of the case. Their statement appeared to have an immediate effect, as the lower court quickly scheduled a hearing and later moved to block the law from implementation.

The law makes it a state crime for migrants to illegally cross the border and allows Texas officials to deport undocumented individuals, though Mexico said Tuesday that it would not accept anyone sent back by the state and condemned the law as “encouraging the separation of families, discrimination and racial profiling that violate the human rights of the migrant community.”

The statute was passed last year amid a record surge in border crossings, as part of Republican Gov. Greg Abbott’s push to expand the state’s role in immigration enforcement — historically part of the federal government’s control over international borders.

The Supreme Court’s decision drew dissent from the three liberal justices, two of whom said the majority was inviting “further chaos and crisis in immigration enforcement.”

“This law will disrupt sensitive foreign relations, frustrate the protection of individuals fleeing persecution, hamper active federal enforcement efforts, undermine federal agencies’ ability to detect and monitor imminent security threats, and deter noncitizens from reporting abuse or trafficking,” wrote Justice Sonia Sotomayor, joined by Justice Ketanji Brown Jackson.

The measure imposes state criminal penalties of up to six months in jail on noncitizens who illegally enter Texas from Mexico. Anyone accused of reentering the country illegally could face felony charges and a 10- to 20-year sentence. Lawmakers also empowered state judges to order deportations to Mexico — without Mexico’s consent — and allowed local law enforcement personnel to carry out those orders. Judges may drop state charges if a migrant agrees to return to Mexico voluntarily.

The litigation over the state law is the latest court battle between the Biden administration and GOP leaders in Texas over the proper role of states in immigration enforcement, which Republicans have emphasized as a key issue in the 2024 presidential campaign. In January, a divided Supreme Court said the Biden administration could remove razor wire that Texas had installed along the U.S.-Mexico border, until the courts determine whether it is legal for the state to erect its own barriers.

White House press secretary Karine Jean-Pierre said Tuesday that the administration fundamentally disagrees with allowing Texas to enforce a “harmful and unconstitutional law” that will “not only make communities in Texas less safe, it will also burden law enforcement, and sow chaos and confusion at our southern border.”

Department of Homeland Security spokesperson Luis Miranda said the department’s agencies, including Customs and Border Protection, do not have authority to assist Texas with the implementation of S.B. 4. The only deportations DHS can conduct involve federal orders, he said.

“Immigration is within the exclusive purview of the federal government,” Miranda said.

The potential effects of S.B. 4 on overall border crossings remain to be seen. Abbott and other Texas officials have claimed in recent months that their state-led crackdown, Operation Lone Star, is already prompting migrants and smugglers to alter their travel plans and head for Arizona or California instead of Texas. Southern Arizona and the San Diego area are now the two busiest places along the Mexican border for illegal crossings, according to the latest U.S. enforcement data.

The area along the Rio Grande where Abbott deployed Texas state troopers and erected razor wire has gone mostly quiet in recent months, the data shows, and illegal entries have remained relatively low in Texas’s Rio Grande Valley, often the southern border’s top gateway for illegal crossings.

A District Court judge last month temporarily blocked the Texas law, saying the statute is probably unconstitutional and “could open the door to each state passing its own version of immigration laws.” Judge David A. Ezra said the law intruded into federal affairs even more than an Arizona immigration law that the Supreme Court partially struck down in 2012.

But the 5th Circuit quickly halted Ezra’s decision, without explanation, and said the law could be enforced, at least temporarily, unless the Supreme Court intervened. The Biden administration, El Paso County and immigrant advocacy groups, all of which had sued to block the law, then asked the Supreme Court to keep it on hold while litigation continues.

As is customary in emergency matters, the majority — Chief Justice John G. Roberts Jr. and Justices Clarence Thomas, Samuel A. Alito Jr. and Neil M. Gorsuch — did not explain their reasons on Tuesday for allowing the law to take effect. But Justice Amy Coney Barrett, joined by Justice Brett M. Kavanaugh, said it was premature for the justices to intervene at the moment, before the 5th Circuit decides whether to keep the law in effect while the appeal is underway. They urged the 5th Circuit to act quickly, and said the Supreme Court would consider additional action if the lower court did not.

That 5th Circuit responded by scheduling Wednesday’s hearing, which will be conducted by Zoom, and then blocking enforcement of the law for now.

Apart from questions about the law’s immediate status, the 5th Circuit has scheduled oral arguments for April 3 to consider its constitutionality.

In their dissent from the Supreme Court’s order, the liberal justices said the 5th Circuit indefinitely upended the status quo last month by halting the lower court’s injunction that blocked the law from taking effect.

“This Court makes the same mistake,” Sotomayor wrote, joined by Jackson, “by permitting a temporary administrative stay to alter the status quo that has existed for over a century.”

Justice Elena Kagan wrote separately and briefly to say that she, too, would have prevented the Texas law from taking effect, noting that immigration, and the entry and removal of noncitizens, “are matters long thought the special province of the Federal Government.”

In response to the Supreme Court’s order, Mexico’s Foreign Ministry expressed concern for “more than 10 million people” of Mexican descent who live in Texas and said the law creates a hostile environment for migrants. The country has been a key partner in the Biden administration’s migration management strategy, and U.S. authorities say lower numbers of illegal crossings over the past two months are partly due to tougher measures from Mexico.

Jorge Dominguez, a staff attorney for El Paso-based Las Americas Immigrant Advocacy Center — one of the groups challenging the law — called the Supreme Court’s order is a gut punch that will impact not only immigrants in Texas but also any state resident of color. Dominguez said his center’s clients, most of whom are immigrants in various types of legal proceedings, have signaled that they will go into hiding and limit their presence in the community if the law takes effect.

“Could I be detained because I’m Brown, speak Spanish fluently and look like someone who crossed into Texas illegally?” mused Dominguez, who is a U.S. citizen. “This law essentially makes anyone like me vulnerable to any law enforcement officer in the state who wants to play the game ‘Guess the Immigrant.’”

Ricardo Samaniego, the top elected official in El Paso County, said he spoke Tuesday about the Supreme Court’s decision with officials in his county and with U.S. Rep. Veronica Escobar (D), who has been a strident critic of Texas’s new law. “The nightmare has become a reality,” Samaniego said, before the 5th Circuit announced it would again block the law. “It’s happened, and it’s something we’ve dreaded for a while.”

Law enforcement agencies across the state, including the Houston Police Department, have said the law threatens their relationship with immigrant communities and may prevent people from calling 911 during emergencies out of fear they could face arrest because of their immigration status. Community organizations have been preparing residents for months with workshops about their constitutional rights to remain silent and the prohibition against unreasonable search and seizure, and what to do if they are arrested.

In urging the high court to block the law from taking effect, Solicitor General Elizabeth B. Prelogar said that it “prevents the Nation from speaking ‘with one voice’ in matters involving foreign affairs” and tramples on federal responsibilities that Congress has laid out. Implementing it, she said, could inflame tensions with Mexico and lead to the deportation of migrants whose lives are in danger, a violation of federal law.

Texas defended its law in part by invoking limited state war powers, suggesting that the influx of immigrants is akin to the imminent danger of an invasion. A provision of the Constitution, which in general prohibits states from engaging in war, includes an exception for when a state is “actually invaded, or in such imminent danger as will not admit of delay.”

The District Court judge in February rejected that argument, writing that “surges in unauthorized immigration alone do not qualify as an ‘invasion.’”

Hernández reported from San Antonio. Nick Miroff and Maria Sacchetti contributed to this report.