Texas immigration law known as SB4, allowing state to arrest migrants, signed by Gov. Greg Abbott

Republican Gov. Greg Abbott of Texas on Monday signed one of the harshest state immigration laws in modern U.S. history, authorizing state officials to arrest and seek the deportation of migrants suspected of crossing the border with Mexico illegally.

The law, known as SB4, gives Texas law enforcement authorities the power to stop, arrest and jail migrants on new, state-level illegal entry charges. It also allows state judges to issue de facto deportation orders against suspected violators of the law, though it's unclear how this provision could be enforced.

Passed by Texas' legislature earlier this year, SB4 is an extraordinary attempt by the state to inject itself into immigration and border enforcement, both longstanding federal prerogatives. It will almost certainly trigger a high-stakes legal and political clash with civil rights groups and potentially the Biden administration. 

"The goal of Senate Bill 4 is to stop the tidal wave of illegal entry into Texas," Abbott said at a signing ceremony along the border in Brownsville. "Senate Bill 4 is now law in the state of Texas."

When does SB4 take effect?

The law is set to take effect in March 2024, though that could change depending on the outcome of one or more legal challenges, the first of which was filed just hours after Abbott's ceremony.

Before it was signed into law, SB4 garnered strong criticism from Democratic lawmakers, the Mexican government and advocacy groups, including the American Civil Liberties Union, which is representing civil rights groups in a lawsuit challenging the law.

The lawsuit, filed in the U.S. District Court for the Western District of Texas, alleges the state is "grasping control over immigration from the federal government and depriving people subject to that system of all of the federal rights and due process that Congress provided to them, including the rights to contest removal and seek asylum."

Asked about SB4, White House spokesperson Angelo Fernández Hernández said, "This is an extreme law that will make communities in Texas less safe. Generally speaking, the federal government — not individual states — is charged with determining how and when to remove noncitizens for violating immigration laws." 

The Justice Department, which would lead the charge in filing any legal action against Texas, declined to comment.

The law is also the latest effort by Texas to challenge President Biden, a Democrat, on immigration. At the direction of Abbott, Texas has bused tens of thousands of migrants to Chicago, New York and other Democratic-led cities. He has also instructed National Guard units and state troopers to repel migrants with razor wire, floating barriers and trespassing arrests.

Stephen Yale-Loehr, a Cornell University professor and immigration expert, called SB4 "unprecedented." He said the Texas law is more sweeping in nature than SB 1070, a controversial Arizona law in 2010 that penalized unauthorized immigrants in different ways, including by empowering state police to stop those believed to be in the country unlawfully. The Supreme Court partially struck down that Arizona law in 2012, concluding that states could not undermine federal immigration law.

"It's by far the most anti-immigrant bill that I have seen," Yale-Loehr said of SB4.

What does SB4 do?

Crossing into the U.S. outside of an official port of entry is already a federal crime, though most migrants' violations are treated as civil cases in the immigration court system. SB4 would make illegal immigration a state crime, ranging from a misdemeanor to a felony.

While Texas troopers have already been arresting some migrant adults on state trespassing charges, that effort has required the consent of private property owners. The new law would not.

Under SB4, crossing into Texas illegally from Mexico would be treated as a misdemeanor crime, punishable by up to 180 days in jail and a fine of up to $2,000. Illegal reentry into Texas would be a felony offense, punishable with up to 2, 10 or 20 years in jail, depending on whether the migrant in question had been previously deported or convicted of certain crimes.

SB4 includes a provision that bars state officials from arresting migrants in certain locations, including schools, places of worship and health care facilities.

The law would also allow Texas magistrates to order migrants suspected of committing the new illegal entry or reentry crimes to return to Mexico as an alternative to continuing their prosecution. Those found to violate those orders could be charged with a second-degree felony.

How Texas would enforce these de facto deportation orders remains unclear, as only the federal government has the facilities, agents and international agreements needed to deport migrants to foreign countries. Mexico's government has said it would reject efforts by Texas to return migrants to its territory.

Abbott and other proponents of SB4 have argued the law is needed to deter illegal border crossings and address what they see as a lackluster effort by the Biden administration to deal with the crisis. More than 2 million migrants were apprehended by U.S. Border Patrol agents along the southern border in both fiscal years 2022 and 2023, the highest levels on record.

But opponents of the measure have denounced SB4 as needlessly punitive, expressing concerns that that the law could lead to racial profiling and sow fear in immigrant communities across the state, not just among new arrivals. They've also argued it will overwhelm state jails and officials, diverting resources away from efforts to arrest serious criminals.