A federal jury has found two Arizona-based trucking companies illegally used Mexican business visas to bypass trade laws.

In a grand jury indictment handed down in U.S. District Court, sworn affidavits show federal agents followed Mexican nationals with B1 visas as they entered the Nogales Border Patrol checkpoint.

From there, they reportedly drove north to business parking lots along the Tucson Airport's western edge to meet U.S. drivers waiting, usually with produce filled 18-wheelers, the drivers switched seats, and the Mexican nationals drove the goods onto Los Angeles and Dallas destinations.

The practice is called "cabotaging," and it's illegal under the North American Free Trade Agreement, which bans B1 drivers from making direct deliveries to U.S. vendors.

American truckers spurred the federal investigation after tipping off Homeland Security that some U.S. trucking companies are paying Mexican drivers $300 to haul the cargo, exactly half the rate legal U.S. truckers command.

In two separate cases, the sting operation in Nogales ensnared two Arizona trucking owners operating as L and R Trucking, Sunset Truck Leasing, and JSJ Enterprises Transportation. Combined, agents said the companies repeated the driver switch nearly 70 times while under observation.

It was the first such surveillance by Homeland Security and agents said they are sharing their findings with other border states where they suspect similar schemes are operating along the U.S.-Mexico border.