DOJ pressed to intervene after controversial Senate Bill 4 signed into law by Gov. Greg Abbott

HOUSTON, Texas (KTRK) -- Senate Bill 4, which is the controversial law that gives local law enforcement in Texas the ability to arrest people they believe are in the country illegally, was signed by Gov. Greg Abbott during a ceremony in Brownsville Monday afternoon.

It won't go into effect until March, but local immigration attorney Raed Gonzalez said he fully expects it to be challenged in the courts.

ABC News obtained a letter from Rep. Joaquin Castro asking the Department of Justice to intervene and prevent SB 4 from going into effect.

The letter was sent to Attorney General Merrick Garland shortly after Abbott signed SB 4, according to ABC News. The letter is also signed by Democrats in the Texas U.S. House Delegation and of the Congressional Hispanic Caucus.

"It opens the door to discrimination," Gonzalez said. "How do you know that somebody's illegally in the country? You have to do racial profiling."

Gonzalez added that the law is also unconstitutional because it gives state judges, in certain instances, the ability to send migrants back to the border and charge them if they don't return to Mexico.

It's the federal government that oversees immigration laws in the United States.

"It appears that the law is unconstitutional, as it is preempted by federal law," Gonzalez said. "I know there are going to be challenges, and this is going to be fought."

ABC13 asked the Houston Police Department and Harris County Sheriff's Office how they plan to enforce SB 4 if it isn't intervened, but both are withholding that information at the moment.

HPD referred Eyewitness News to its racial profiling policy that prohibits the practice within the department.

Gonzalez said the law doesn't require police departments to enforce it, but he doesn't expect HPD to do it voluntarily because their plates are already full.

"They're not going to have time to enforce immigration laws," Gonzalez said.

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