Sinister Diesel, a California-based truck parts manufacturer, has been slapped with a heavy fine for selling devices that defeat a vehicle’s emissions controls.

For 10 years, Sinister manufactured and sold “delete devices” or “defeat devices” that allow vehicles like diesel trucks to dramatically increase the amount of pollutants they put in the air. The practice, often referred to as “rolling coal,” can cause engines to emit massive black clouds of exhaust fumes.

According to the U.S. Justice Department, Sinister also sold “delete kits” that sometimes came bundled with “delete tunes,” third-party software that can make a vehicle with defeated emissions controls appear to run normally. The company is also accused of advising customers on the deleting process and on how to get around state emissions tests.