A federal judge in San Antonio is hearing arguments today in a lawsuit filed by several cities, including Austin, seeking to block enforcement of the state's new anti-sanctuary cities law, Senate Bill 4.

U.S. District Judge Orlando Garcia will rule on whether SB 4 should be allowed to take effect Sept. 1 while a court battle plays out. The bill, signed by Gov. Greg Abbott in May, requires jurisdictions to honor all requests from Immigration and Customs Enforcement to detain suspected undocumented immigrants and allows local law enforcement officials to question a person's immigration status during a routine stop. It also punishes officials who do not cooperate with federal immigration laws.

Supporters argue SB 4 will increase public safety. Opponents say it violates the U.S. Constitution by threatening free speech and equal protection.

Inside the courtroom, Judge Garcia asked how SB 4 would be enforced, for example, whether an officer could ask all passengers in a car about their immigration status and if local police could make immigration sweeps.

The bill's author, Republican state Sen. Charles Perry of Lubbock, said he’s confident it will pass constitutional muster.

“It’s going to be a real stretch to find an unconstitutional issue inside the bill because everything inside the bill is current law,” he said. “We were just telling law enforcement officials they have to comply or cooperate.”

Austin joined the suit, which was originally filed last month by the City of San Antonio, on June 2. Since then, Dallas and Houston have also signed on.

On the steps of the courthouse, elected officials from cities across Texas rallied in opposition to SB 4. Austin Mayor Steve Adler repeated his argument that it makes cities less safe by discouraging immigrants to report crimes and serve as witnesses.

"We have spent six months where the safety of cities has been tossed around like a political football," he said. "Finally, we are in a forum where facts and law carry the day.”

“We are united in trying to seek a preliminary injunction on a law that would divide our community, divide communities throughout the state of Texas," San Antonio’s newly elected mayor Ron Nirenberg said.

Garcia is not expected to issue a ruling immediately.On Friday, the U.S. Department of Justice filed a statement of interest in the case, officially throwing its support behind the State of Texas and Attorney General Ken Paxton. The DOJ argues SB 4 is valid and does not violate the Constitution.

The day after Abbott signed the bill, Paxton filed a preemptive lawsuit, asking a court to declare SB 4 constitutional. A federal court in Austin is set to consider that request Thursday.

KUT's Audrey McGlinchy spoke with Morning Edition host Jennifer Stayton about the case.

Reporter Ryan Poppe of Texas Public Radio contributed to this report.

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