AUSTIN, Texas (AP) — A federal judge on Thursday voiced concerns over a Texas law that would give police broad authority to arrest migrants on charges of illegal entry starting in March, saying it would be a “nightmare” if the U.S. became a patchwork of states enforcing different immigration laws.

“That turns us from the United States of America into a confederation of states,” said U.S. District Judge David Ezra, who did not immediately issue a ruling. “That is the same thing the Civil War said you can’t do.”

Ezra is considering a lawsuit filed by the U.S. Justice Department in what is the first legal test of what opponents have called the most dramatic attempt by a state to police immigration since a 2010 Arizona law that was partially struck down by the Supreme Court. It is among several courtroom battles Texas is fighting with President Joe Biden’s administration over how far the state can go to try to prevent migrants from crossing the border.

The judge remained skeptical during the nearly three-hour hearing in Austin, often sharply questioning the lawyers defending the law that was signed by Republican Gov. Greg Abbott.

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AP AUDIO: Judge expresses skepticism at Texas law that lets police arrest migrants for illegal entry.

A federal judge has voiced concerns over a Texas law that would give police broad authority to arrest migrants on charges of illegal entry. AP’s Lisa Dwyer has the story.

Ezra, who was appointed by former President Ronald Reagan, did not say exactly when he would rule but said he hoped to give enough time for any appeals before the law takes effect March 5.

The measure would allow any Texas law enforcement officer to arrest people who are suspected of entering the country illegally. Once in custody, they could either agree to a Texas judge’s order to leave the U.S. or be prosecuted on a misdemeanor charge of illegal entry. Migrants who don’t leave could be arrested again and charged with a more serious felony.

Ezra noted he has experience hearing cases that deal with border issues and is familiar with the concerns raised by Abbott and other state officials over illegal crossings. But he said he was “not buying into” the argument that only criminals are coming across the border, calling the “vast majority” of the migrants who enter the U.S. without permission otherwise law-abiding people.

He also questioned whether empowering local judges to remove people from the U.S. could interfere with federal processes or protections.

The state pointed to declarations by police officials who would enforce the law. Ezra responded: “I have to rule on what the law says, not what they say they will or won’t do.”

Ezra became frustrated during an exchange with an attorney for the state who said people with pending asylum cases who were arrested under the law would not be removed from the country, per their federal protections.

“You just go to jail?” Ezra asked.

“Yes,” replied Ryan Walters, chief of the Texas Attorney General’s Office special litigations division, moments after saying there is “no safer place” than a state prison for a migrant to await an immigration court case.

For months, tensions have escalated between the Biden administration and Texas over who can patrol the border and how. The Justice Department also has taken Texas to court over a floating barrier in the Rio Grande and defended the ability of U.S. Border Patrol agents to cut through and remove miles of razor wire that the state has installed along the border.

Republican governors across the U.S. have backed Abbott’s efforts. A heavy presence of Texas National Guard members in the border city of Eagle Pass has denied Border Patrol agents access to a riverfront park. The agents had previously used the park for monitoring and patrols, as well as to process migrants who made it across the Rio Grande to U.S. soil.

Civil rights groups have argued that the new law, known as Senate Bill 4, could lead to civil rights violations and invite racial profiling.

Republicans have defended the law by saying it would likely only be enforced near the U.S.-Mexico border. They also contend that it would not be used to target immigrants who have long been settled in the U.S. because the statute of limitation on the misdemeanor charge is two years.