Two environmental groups have recently filed a lawsuit against the U.S. Environmental Protection Agency (EPA) accusing it of delaying smog reduction measures in six states with some of the nation’s worst air quality.

The lawsuit, filed by the Center for Biological Diversity (CBD) and the Center for Environmental Health (CEH), alleges that the EPA failed to address the lack of regional planning to resolve violations of the 2008 National Ambient Air Quality Standards for ozone, a Jan. 5 CBD press release said.

“The EPA’s failure to do its part to cut smog pollution has very dangerous consequences for the people and wildlife living in these areas,” Victoria Bogdan Tejeda, staff attorney at CBD, said in the release. “The Clean Air Act saves lives, but only if federal regulators enforce it.”

The regions mentioned in the lawsuit are the “Chicago-Naperville area of Illinois; Dallas-Fort Worth area of Texas; New York City metro areas of Connecticut, New York and New Jersey; non-metro areas of Connecticut; and San Diego County, California,” the release said. The affected regions have a combined population of 42 million.

Ozone pollution has been linked to several negative effects, including those on human health and climate change, the release said.

“The EPA’s failure to enforce smog protections increases the risk of asthma attacks and other serious health problems in all of these communities,” Kaya Allan Sugerman, director of Illegal Toxic Threats at CEH, said in the release. “Federal and state regulators need to quit turning their backs on this critical work.”