GRAND RAPIDS, Mich. (Michigan News Source) – U.S. Attorney General for the Western District of Michigan Mark Totten announced that three companies and eleven individuals have been charged with violating the Clean Air Act. The case is one of the largest of its kind charged in the United States.

MORE NEWS: Crews Clean Up Styrofoam Along Lake Superior

“Today’s criminal charges sent a loud message of accountability to polluters who flout our environmental laws,” Totten said in a Wednesday press release. “These rules not only protect the planet; they also protect people—especially the most vulnerable.”

The defendants are charged with participating in an aftermarket scheme to disable the emissions control systems of semitrucks. Two of the corporate defendants, Accurate Truck Service and Diesel Freak, changed hardware components and computer systems of the trucks’ emissions systems to improve performance and fuel economy. The third corporate defendant, Griffin Transportation, hired them to “delete” trucks they owned from their records. Over 400 “deletions” have been traced to the defendants.

“To the owners and drivers of the vehicles that participated in this scheme and are now spewing harmful pollutants: get them fixed now,” Totten said.

Acting Special Agent in Charge Richard Conrad of the EPA’s Criminal Investigation Division said that tampering with the emissions controls released “toxic gases and impurities” from diesel exhaust. “This case highlights EPA and our law enforcement partners’ continued efforts to prosecute those who violate environmental and public health laws in the U.S. for financial gain,” he said.

The EPA is investigating the case alongside Homeland Security Investigations, the U.S. Department of Transportation, Office of Inspector General, and the Michigan Department of Natural Resources, Environmental Investigation Section.