Texas Lt. Gov. Dan Patrick on Wednesday asked the state’s attorney general to determine if the chief of the San Antonio Police Department violated the state’s immigration-enforcement law during a human smuggling incident.

Late last month, San Antonio Police Chief William McManus said officers arrested the driver of a tractor-trailer after a passerby saw people being unloaded from the vehicle and flagged down a police unit, the San Antonio Express-News reported.

Officers charged Herbert Nichols, 58, under a state statute that makes knowingly transporting persons in the country illegally a crime, instead of turning the case over to federal agents with Immigration and Customs Enforcement. The immigrants were interviewed and released to a Catholic charity.

During a subsequent news conference, McManus said it could have been a state or federal charge but that he chose to go with the state charge because officers were waiting to see how to move forward.

In a letter, Patrick asked Attorney General Ken Paxton to investigate whether the department violated any portion of the state’s Senate Bill 4, a controversial and sweeping immigration enforcement bill passed by the Texas Legislature last year.

“I am very troubled by the recent news reports of the San Antonio police chief releasing suspected illegal immigrants in a case of human trafficking or human smuggling without proper investigation, identification of witnesses, or cooperation with federal authorities,” Patrick wrote. “Such action could be in direct violation of the recently passed Senate Bill 4 and threatens the safety of citizens and law enforcement.”

It’s unclear exactly which provision of the SB 4 Patrick alleges McManus could have violated. As passed, SB 4 allows local law enforcement officers to question the immigration status of people they detain or arrest and punishes local government department heads and elected officials who don’t cooperate with federal immigration "detainers" — requests by agents to turn over immigrants subject to possible deportation — in the form of jail time and fines.

It also mandates that local entities exchange immigration information they obtain with federal officials and allows for a citizen complaint to be lodged against an entity thought to be in violation of any of SB4's provisions. Patrick stated that should such action be taken in this case, he asked Paxton to "act swiftly to ensure San Antonio Police Department is in compliance with the law."

But SB 4 is currently tangled up in litigation after several local governmental entities, including the city of San Antonio and Bexar County, filed suit to stop it.

In late August, U.S. District Judge Orlando Garcia halted several parts of the law, including the provision that requires jail officials to honor all detainers. He also blocked sections that prohibit local entities from pursuing or endorsing “a pattern or practice that 'materially limits' the enforcement of immigration laws” and another that prohibits “assisting or cooperating” with federal immigration officers as reasonable or necessary.

But a panel of the 5th Circuit Court of Appeals in New Orleans ruled the detainer provision could stand until an ultimate determination is made on the merits of the case. The panel also determined that law enforcement officers, including campus police, with “authority that may impact immigration” cannot be prevented from assisting federal immigration officers. That ruling is what’s on the books until a final decision on Garcia’s injunction is made.