The Biden administration has issued a warning to Texas Governor Greg Abbott, stating that legal action will be taken if the state enforces a new law allowing authorities to arrest, jail, prosecute, and deport migrants who enter the country illegally. The law, known as SB4 or Senate Bill 4, is part of the state's Operation Lone Star and is set to go into effect on March 5. However, the Justice Department has deemed the law unconstitutional and contrary to the US commitment to processing noncitizens in line with the Immigration and Nationality Act.

In a letter sent to Abbott, Principal Deputy Assistant Attorney General Brian M. Boynton states, "SB 4 is preempted and violates the United States Constitution. Accordingly, the United States intends to file suit to enjoin the enforcement of SB 4 unless Texas agrees to refrain from enforcing the law." The letter argues that SB 4 infringes upon the federal government's authority and could lead to migrants with legitimate asylum claims being imprisoned or deported to countries where they may face persecution or torture.

SB 4 makes illegally entering the US from Mexico a state crime and grants police the authority to arrest individuals suspected of crossing the Rio Grande between ports of entry. Migrants caught illegally entering the country would face a Class B misdemeanor charge, carrying a punishment of up to six months in jail. Repeat offenders would face a second-degree felony charge, punishable by up to 20 years in prison. However, the law also allows Texas judges to drop charges against migrants if they agree to be deported.

The Biden administration has requested that Abbott confirm by January 3 that he will not enforce the new law. In response, Abbott criticized President Biden, accusing him of "destroying America" and claiming that Texas is trying to save the rule of law. A spokesperson for Abbott stated that Texas is prepared to take the legal battle over enforcing SB 4 to the Supreme Court if necessary, citing President Biden's "dangerous inaction" at the southern border.

SB 4 is already facing legal challenges, with the American Civil Liberties Union arguing that the law is unconstitutional. If implemented, SB 4 would be the strictest state immigration law in modern US history, criminalizing unauthorized immigration and allowing for varying degrees of punishment depending on the offense. Critics of the law have raised concerns about racial profiling and the potential strain on state and local jails. The Mexican government has also voiced opposition to SB 4, stating that it will not accept returns of migrants from Texas officials and denouncing the law as "anti-immigrant.".