MARISSA, Ill. (WTVO) — A well-known environmental group is suing an Illinois energy company for allegedly running a coal plant without a permit.

The Sierra Club said that Prairie State’s coal plant in Downstate Illinois emitted more carbon dioxide than two million cars last year, operating without the right permit to monitor those levels the entire time it has been open.

Local residents would not be warned when pollution levels from the plant exceed certain thresholds without the permits.

“This plant is now one of the largest sources of air pollution in the country,” said Christine Nannicelli of the Beyond Coal Campaign. “In addition to costing far more originally touted to municipalities, the pollution impacts received from the plant show how far the myth of a clean coal facility is from reality.”

Prairie State called Sierra Club’s lawsuit politically motivated. They said that they are operating legally under a permit from the Illinois Environmental Protection Agency that required them to install a $1 billion emissions control system.