A federal appeals court has cleared the way for Texas to enforce a 2023 immigration law that allows state and local police to arrest people suspected of entering the United States illegally, reviving one of the country’s most closely watched battles over state power at the southern border.

The ruling from the 5th U.S. Circuit Court of Appeals, issued Friday and drawing renewed attention Monday, lifts a lower-court injunction that had kept Senate Bill 4 from taking effect for most of its legal life. The decision means Texas may proceed with a law that creates state criminal penalties for illegal entry and reentry, while authorizing state judges to order some defendants to leave the country.

The appeals court did not decide the core constitutional question that has followed SB 4 since its passage: whether Texas may create and enforce its own immigration-related criminal system in an area historically controlled by the federal government. Instead, the court’s en banc majority concluded that the remaining challengers — including El Paso County and immigrant-rights organizations — had not shown the legal injury needed to keep the case alive.

That procedural holding is consequential. The Biden administration originally sued Texas to block the law, arguing that SB 4 conflicted with federal immigration law and intruded on the national government’s authority over foreign affairs and removal decisions. But after President Donald Trump returned to office, the federal government withdrew from the challenge, leaving local and private plaintiffs to carry the case.

Texas officials cast the decision as a validation of the state’s border enforcement strategy. Attorney General Ken Paxton said his office had secured a major victory defending SB 4 before the full 5th Circuit, describing the measure as a law that “creates state crimes that track federal immigration crimes” and empowers police to arrest people accused of unlawful entry or reentry.

Gov. Greg Abbott signed SB 4 in December 2023 after Texas lawmakers passed it during a period of intense political conflict over border crossings, asylum processing and the state’s Operation Lone Star enforcement campaign. The law was designed to make illegal entry into Texas a state misdemeanor, with enhanced penalties for repeat offenses, and to permit state judges to issue orders requiring defendants to return to the country from which they entered.

Opponents say that structure effectively creates a parallel state immigration system. The American Civil Liberties Union and other groups said the 5th Circuit ruling turned on procedure rather than a finding that SB 4 is constitutional. They warned that the law could expose Texans to unlawful stops, racial profiling and mistaken detention, including for U.S. citizens and lawful residents who may be perceived by officers as undocumented.

The legal fight has moved through a complicated series of rulings since 2024. A federal district judge initially blocked SB 4, finding that immigration enforcement is primarily a federal function and that Texas could not override federal priorities. The U.S. Supreme Court briefly allowed the law to take effect in March 2024 while the appeals process continued, but the 5th Circuit quickly restored a pause. A three-judge panel later kept the injunction in place before the full appeals court reheard the case.

The new 5th Circuit decision reverses that posture. The majority said the plaintiffs had not established standing under Article III of the Constitution, meaning they could not proceed in federal court without showing a sufficiently concrete and particularized injury traceable to SB 4. Because the court resolved the case on standing grounds, it said it did not need to address whether SB 4 is preempted by federal immigration law.

Dissenting judges objected sharply, warning that the ruling allows a sweeping immigration measure to go into effect without resolving whether it conflicts with federal law. Critics of the law have pointed to the Supreme Court’s 2012 decision in Arizona v. United States, which limited state efforts to create immigration-enforcement schemes that interfere with federal authority.

For police agencies in Texas, the immediate practical effect remains uncertain. The law gives officers power to arrest people suspected of illegal entry, but implementation could vary across jurisdictions and may depend on state guidance, local policies and the willingness of prosecutors and judges to pursue cases. The ruling also arrives as Texas cities continue to face pressure from state officials over cooperation with federal immigration authorities.

Houston recently amended a local policy limiting police cooperation with U.S. Immigration and Customs Enforcement after Abbott and Paxton warned the city could lose public safety funding. That fight, separate from SB 4, underscored how immigration enforcement is increasingly shaping state-local relations in Texas, including in large cities that have expressed concern about constitutional limits and community trust.

Mexico has previously objected to state-level deportation mechanisms, and SB 4’s return-order provisions could again raise diplomatic and logistical questions. Removal from the United States is normally handled through federal immigration proceedings, with federal agencies coordinating custody, deportation and international arrangements. State court orders directing people to return across the border would push Texas into territory the federal government and immigration advocates have long argued belongs exclusively to Washington.

The case is also likely to influence other states. Republican-led states have watched Texas’ border litigation closely as they test how aggressively they can police immigration inside state criminal systems. A final green light for SB 4 could encourage similar laws elsewhere, while renewed challenges could produce another major appellate or Supreme Court fight over the division of immigration authority.

For migrants and border communities, the decision adds new uncertainty. Civil-rights groups say people may avoid reporting crimes, seeking medical care or interacting with public agencies if they believe routine encounters with police could trigger immigration-related arrest. Supporters counter that Texas needs additional enforcement tools because federal policy has failed to deter unlawful crossings and because border communities have borne the costs of illegal entry.

The 5th Circuit ruling does not end the broader legal conflict. New plaintiffs could attempt to challenge the law after enforcement begins, or existing opponents could seek further review. But for now, the decision gives Texas its clearest opening yet to implement SB 4 and marks a major turn in the national debate over whether states can directly police unlawful entry into the United States.