The Biden administration on Thursday warned Texas that it will sue the state if it implements a strict immigration law known as SB4 that would empower state and local law enforcement officials to arrest, jail and prosecute migrants suspected of entering the U.S. unlawfully.

The Justice Department said it would file a lawsuit against SB4 if Texas did not assure federal officials by Jan. 3 that the state would refrain from enforcing the law as planned in March, according to a letter sent to Gov. Greg Abbott on Dec. 28 and obtained by CBS News. In addition to creating illegal entry crimes at the state level, the law would allow Texas judges to issue de facto deportation orders.

In its letter, the Justice Department said SB4 would effectively criminalize actions that are already illegal at the federal level, undermine relations with Mexico and prevent officials from enforcing federal immigration laws, including those designed to grant refuge to migrants fleeing persecution. 

"Because SB 4 is unconstitutional and will disrupt the federal government's operations, we request that Texas forbear in its enforcement," Principal Deputy Assistant Attorney General Brian Boynton said in his letter to Abbott.

If Texas does not heed the Biden administration's demand, "the United States intends to file suit to enjoin the enforcement of SB 4," Boynton warned.

In a social media post on Thursday, Abbott, who signed SB4 earlier this month after the measure was passed by the Texas legislature, said the Biden administration's legal threat showed "hostility to the rule of law in America."

The Biden administration, he added, "not only refuses to enforce current U.S. immigration laws, they now want to stop Texas from enforcing laws against illegal immigration."

Renae Eze, a spokeswoman for Abbott, said Texas is prepared to defend SB4 before the Supreme Court.  

SB4 is already being challenged in federal court by the American Civil Liberties Union, which has also argued the law is unconstitutional.

What would SB4 allow Texas to do?

SB4 is the latest attempt by Texas to challenge President Biden on immigration. Under Abbott, Texas has transported tens of thousands of migrants to New York City, Chicago and other Democratic-led cities, tasked National Guard units to fortify the Rio Grande with razor wire and assigned state troopers to arrest some migrants on trespassing charges.

The measure would be the strictest state immigration law in modern U.S. history, making unauthorized immigration a state crime, ranging from a misdemeanor to a felony.  

Entering 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 would also allow Texas magistrates to order migrants suspected of violating the illegal entry or reentry laws 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.

The Mexican government has already said it would not accept returns of migrants from Texas state officials, denouncing SB4 as an "anti-immigrant" law.

Abbott and other supporters of SB4 have argued the law will deter illegal border crossings. He and other Republican leaders have faulted the Biden administration for the unprecedented levels of migrant crossings recorded over the past three years.

But critics of the law have said it will lead to racial profiling of people who look like migrants. They've also argued SB4 could backfire from a public safety perspective, overwhelming state and local jails and diverting law enforcement officials away from efforts to arrest serious criminals.

Read the full letter below:

In:
• Immigration
• Texas
• U.S.-Mexico Border

Camilo Montoya-Galvez

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

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