Truck owners sued Ford in federal court Wednesday for apparently rigging 500,000 diesel pickup trucks to cheat U.S. emissions tests.

The drivers accuse Ford of "knowingly installing emissions-cheating software devices” in F-250 and F-350 Super Duty models, although the company marketed the trucks as “the cleanest super diesel ever.”

The suit, filed in U.S. District Court for the Eastern District of Michigan, says the trucks emit nitrogen oxide pollutants at 50 times the legal limit.

The suit also includes German auto supplier Robert Bosch as a defendant.

Ford denied any wrongdoing.

“All Ford vehicles, including those with diesel engines, comply with all U.S. EPA and CARB emissions regulations,” Daniel Barbosa, a spokesman for Ford, told Bloomberg. “Ford vehicles do not have defeat devices. We will defend ourselves against these baseless claims.”

Ford is at least the fifth car company accused of cheating on emissions tests.

Volkswagen started the scandal in 2015 when the company admitted it sold “clean diesel” vehicles containing software designed to cheat U.S. emissions tests.

The automaker faced federal prosecution in the U.S., costing Volkswagen more than $30 billion.