The 5th U.S. Circuit Court of Appeals kept Senate Bill 4 — a sweeping Texas immigration policy — on hold Wednesday after hearing from both state and federal attorneys.

During Wednesday's hour-long hearing, a three-judge panel listened to arguments on S.B. 4, which would authorize law enforcement officers in the state to arrest, detain and deport people suspected of entering the U.S. in Texas from Mexico without legal authorization. It's not clear when the appeals court will hand down a decision, though whatever it decides is likely to be appealed to the U.S. Supreme Court.

"This is going to be a massive new system if it's allowed to go into effect," said Cody Wofsy, an attorney representing the ACLU of Texas. The ACLU of Texas is one of several plaintiffs suing Texas over S.B. 4. The legal challenges brought by the ACLU, the Texas Civil Rights Project, El Paso County, American Gateways and El Paso-based Las Americas Immigrant Advocacy Center were combined with a lawsuit brought by the U.S. Department of Justice.

Advocates say S.B. 4 is unconstitutional because the federal government, not the state, has authority over immigration. Texas counters that it has a responsibility to secure its border and that the Biden administration has been derelict in its duty.

Federal prosecutors on Wednesday said S.B. 4 interferes with federal border enforcement and harms its relationship with Mexico.

Mexico's federal government has condemned S.B. 4 — both in statements and a brief filed with the 5th Circuit — as a policy that would criminalize migrants and encourage "the separation of families, discrimination and racial profiling that violate the human rights of the migrant community."

"Mexico categorically rejects any measure that allows state or local authorities to exercise immigration control, and to arrest and return nationals or foreigners to Mexican territory," the country's Ministry of Foreign Affairs said in a statement in March.

State lawmakers passed S.B. 4 in November. The law establishes criminal penalties for anyone suspected of crossing into Texas from Mexico other than through an international port of entry. The penalties range from a Class B misdemeanor to a second-degree felony.

A legal back-and-forth resulted in the law taking effect on March 5 for about nine hours before an injunction was reinstated.

In arguing that Texas should not be preempted from enforcing S.B. 4, Texas Solicitor General Aaron Nielson said the law works hand and hand with federal immigration law.

"Now to be fair, maybe Texas went too far," Nielson said at the outset of the proceeding Wednesday. "And that's the question this court is going to have to decide."

Nielson said state and federal officials would work together to carry out the law's removal provisions. State troopers would turn offenders over to federal authorities, not conduct formal deportations to Mexico, he said.

"That's not how it's going to be," Nielson said. "It's going to be people are taken to the port of entry, and the United States controls the port of entry."

The law doesn't state how troopers should carry a magistrate judges for an offender "to return to the foreign nation from which the person entered or attempted to enter," according to the bill text.

Jorge Dominguez, staff attorney with Las Americas, told USA TODAY, "Texas is just making an argument to please the court. It’s not on the books. It’s not in the law itself."

Contributed: Lauren Villagran