The U.S. Department of Justice says it will sue Texas if the state enforces a new law enacted this month allowing state officials to arrest and deport people who come into the U.S. illegally.

In a letter to Texas Gov. Greg Abbott, the justice department said Texas' new law, SB4, oversteps into federal immigration jurisdiction and is unconstitutional.

"SB4 effectively creates a separate state immigration scheme by imposing criminal penalties for violations of federal provisions on unlawful entry... and by authorizing state judges to order the removal of noncitizens from the United States. SB4 therefore intrudes into a field that is occupied by the federal government and is preempted," wrote Principal Deputy Assistant Attorney General Brian M. Boynton in a letter to Abbott obtained by USA TODAY.

If Texas begins enforcing the law, the federal government will sue to block the law in court, Boynton said.

SB4, which Democratic state leaders in Texas warned could lead to racial profiling, is set to take effect in March.

Texas has until Jan. 3 to let federal officials know if the state will go forward with planned enforcement of the law, Boynton's letter says.

On X, formerly Twitter, Abbott characterized it as "hostility to the rule of law in America."

Texas civil rights organizations and El Paso County have already sued the Texas Department of Public Safety in protest of the law.

The ACLU filed the lawsuit in U.S. District Court for the Western District of Texas in Austin on behalf of El Paso County and two immigrant advocacy organizations, El Paso's Las Americas Immigrant Advocacy Center and Austin-based American Gateways.

The justice department's warning comes two days after officials in New York City announced new restrictions for buses transporting migrants to the city sent by Abbott. In recent years, Abbott has sent more than 30,000 migrants to New York City alone, the Houston Chronicle reported Thursday.

“New York City has begun to see another surge of migrants arriving, and we expect this to intensify over the coming days as a result of Texas Governor Abbott’s cruel and inhumane politics,” Mayor Eric Adams said Wednesday.

What would Texas' SB4 do?

SB4 makes it a state crime to circumvent traditional immigration checkpoints and illegally cross into the U.S.

The law, signed by Abbott on Dec. 18, gives police in Texas the power to arrest anyone they suspect may have crossed the border illegally.

The law would also give state judges the power to deport individuals who appear in court on charges of illegally entering the U.S.

The day the law was enacted, Texas leaders sent a letter to the justice department expressing concern SB4 could lead to the unlawful arrest of U.S. citizens and lawful residents suspected of being immigrants by police.

"In practice, this would place people with authorization to be in the United States, even United States citizens, at risk of being forced to leave Texas," Democratic lawmakers wrote.

SB4 follows Abbott's Operation Lone Star

Abbott's enactment of SB4 comes after the governor in 2021 launched Operation Lone Star, a border security initiative that places thousands of state troopers and Texas National Guard members along the southern border with Mexico.

The operation allows state troopers and national guard members to assist federal authorities in arresting people for illegally crossing into the U.S.

The initiative has also been criticized because Texas state officials don't have the final say in enforcing immigration law, which rests with the federal government.