The EPA is violating the federal Clean Air Act in Arizona, according to a lawsuit filed by the Sierra Club. 

The complaint, filed Tuesday in federal court, says the EPA failed to follow through on Arizona’s state implementation plan in west Pinal County for fine particle pollution.

The complaint also says the EPA is failing to determine whether or not the area in Pinal County is improving or meeting air quality standards since determining in 2012 that it was not.

In 2012, the EPA designated the county as a “nonattainment” area for particulate matter, and a plan was put in place. According to the Sierra Club’s lawsuit, west Pinal County’s pollution levels are among the worst in the nation.