The U.S. Border Patrol is monitoring millions of American drivers nationwide in a secretive program to identify and detain people whose travel patterns it deems suspicious, The Associated Press has found.

The Border Patrol’s predictive intelligence program has resulted in people being stopped, searched and in some cases arrested. A network of cameras scans and records vehicle license plate information, and an algorithm flags vehicles deemed suspicious based on where they came from, where they were going and which route they took. Federal agents in turn may then flag local law enforcement.

Suddenly, drivers find themselves pulled over — often for reasons cited such as speeding, no turn signals or even a dangling air freshener blocking the view. They are then aggressively questioned and searched, with no inkling that the roads they drove put them on law enforcement’s radar.

In 2022, Alek Schott, from Houston, had his car searched from top to bottom by Texas sheriff’s deputies outside San Antonio after they got a tipoff from Border Patrol agents.

Federal agents observed that Schott, who works in the oil industry, had made an overnight trip from Houston to Carrizo Springs, Texas, and back, court records show. They knew he stayed overnight in a hotel about 100 miles from the U.S.-Mexico border. They knew that in the morning Schott met a female colleague there before they drove together to a business meeting in a border town.

At Border Patrol’s request, Schott was pulled over by Bexar County sheriff’s deputies. The deputies held Schott by the side of the road for more than an hour, searched his car and found nothing.

According to testimony and documents released as part of Schott’s lawsuit, sheriff’s deputy Joel Babb was on a group chat with federal agents called Northwest Highway sharing tips. On the bodycam video during Schott’s stop, Babb could be heard saying it was one of “the intel stops of a one-day turnaround.”

Babb did not respond to multiple requests for comment from AP. The Bexar County sheriff’s office declined to comment due to pending litigation and referred all questions about the Schott case to the county’s district attorney. The district attorney did not respond to a request for comment.

“I didn’t know it was illegal to drive in Texas,” Schott said in an interview with the AP. His case is pending in federal court in Texas.

The Border Patrol’s parent agency, U.S. Customs and Border Protection, said they use license plate readers to help identify threats and disrupt criminal networks and are “governed by a stringent, multi-layered policy framework, as well as federal law and constitutional protections, to ensure the technology is applied responsibly and for clearly defined security purposes.”

“For national security reasons, we do not detail the specific operational applications,” the agency said.

While the Border Patrol primarily operates within 100 miles of the border, it is legally allowed “to operate anywhere in the United States,” the agency added.

Once limited to policing the nation’s boundaries, the Border Patrol’s surveillance system stretches into the country’s interior and monitors ordinary Americans’ daily actions and connections for anomalies instead of simply targeting wanted suspects. Started about a decade ago to fight illegal border-related activities and the trafficking of both drugs and people, it has expanded over the past five years. Under the Trump administration’s heightened immigration enforcement efforts, CBP is now poised to get more than $2.7 billion to build out border surveillance systems such as the license plate reader program by layering in artificial intelligence and other emerging technologies.

While collecting license plates from cars on public roads has generally been upheld by courts, some legal scholars see the growth of large digital surveillance networks such as Border Patrol’s as raising constitutional questions.

“They are collecting mass amounts of information about who people are, where they go, what they do, and who they know,” said Nicole Ozer, the executive director of the Center for Constitutional Democracy at UC Law San Francisco. “That very surveillance infrastructure is actually being weaponized to attack community members, to threaten the rights and safety of individuals.”

Schott warns that for every success story touted by Border Patrol, there are far more innocent people who don’t realize they’ve become ensnared in a technology-driven enforcement operation.