Just hours after the Supreme Court granted Texas officials permission to arrest and prosecute migrants suspected of crossing the U.S. southern border without authorization, an appeals court late Tuesday blocked the state from enforcing its controversial immigration law known as SB4.

In a late-night order, a 5th Circuit Court of Appeals panel dissolved a pause that it issued in early March to suspend a lower court ruling that found SB4 to be unconstitutional. The order reinstated a ruling from U.S. District Court Judge David Ezra, who concluded in late February that SB4 conflicted with federal immigration laws and the Constitution.

Earlier on Tuesday, the Supreme Court denied a request from the Justice Department to void the initial 5th Circuit order that had paused Ezra’s ruling. The high court allowed SB4 to take effect for several hours, though it’s unclear whether Texas arrested any migrants under the law during that short time span.

Ezra’s order blocking SB4 will stay in place until the 5th Circuit rules on Texas’ request to allow the law to be enforced while the appeals court considers its legality. A virtual hearing on that question is scheduled for Wednesday morning.

Passed by the Texas legislature last year, SB4 criminalizes unauthorized migration at the state level, making the act of entering the U.S. outside of a port of entry — already a federal offense — into a state crime. It also creates a state felony charge for illegal reentry.

SB4 empowers law enforcement officials in Texas, at the state and local level, to detain and prosecute migrants on these new criminal charges. It also grants state judges the power to require migrants to return to Mexico as an alternative to prosecution.

The Justice Department has said SB4 conflicts with federal law and the Constitution, noting that immigration enforcement, including arrests and deportations, have long been a federal responsibility. It has also argued the measure harms relations with the Mexican government, which has denounced SB4 as “anti-immigrant” and vowed to reject migrants returned by the state of Texas.

Texas Gov. Greg Abbott, who has positioned himself as the leading state critic of President Biden’s border policies, has portrayed SB4 as a necessary measure to discourage migrants from crossing the Rio Grande, arguing the federal government has not done enough to deter illegal immigration.

Over the past three years, Texas has mounted the most aggressive state effort yet to challenge the federal government’s power over immigration policy, busing tens of thousands of migrants to major, Democratic-led cities, assembling razor wire and buoys along stretches of the border to deter migrant crossings, and filing multiple lawsuits against federal immigration programs.

Camilo Montoya-Galvez

Camilo Montoya-Galvez is the immigration reporter at CBS News. Based in Washington, he covers immigration policy and politics.