SAN FRANCISCO (CN) — A lawsuit filed Thursday could force the Biden administration to crack down on air pollution in some of the smoggiest areas of the nation, including New York, Dallas and Chicago.

The Center for Biological Diversity and three other groups claim the U.S. Environmental Protection Agency has been dragging its feet in lowering smog ratings in eight zones where nearly 50 million people reside.

Downgrading air quality ratings in those regions from “serious” to “severe” would trigger stricter pollution limits, according to Robert Ukeiley, a senior attorney at the Center for Biological Diversity.

“Each day that EPA delays this has long-term consequences as far as how much pollution people will be exposed to in these areas,” Ukeiley said in a phone interview Thursday.

According to the lawsuit, the EPA missed a deadline this past January to decide whether or not the eight regions met benchmarks for air quality improvement.

The eight regions named in the lawsuit Include Chicago-Naperville area of Illinois; Dallas-Fort Worth and Houston-Galveston-Brazoria in Texas; New York City metro areas of Connecticut, New York and New Jersey; non-metro areas of Connecticut; the Denver-Boulder-Greeley-Fort Collins-Loveland area of Colorado; and western Nevada County and Ventura County in California.

“Clean air delayed is clean air denied,” said Jeremy Nichols of co-plaintiff WildEarth Guardians in a statement Thursday.

Air pollution has been known to cause or exacerbate conditions like asthma. It’s also been linked to diminished lung function, respiratory ailments, emergency room visits, respiratory-related hospital admissions and premature death.

It can also damage vegetation and commercial crops and harm the ecosystem, according to the lawsuit.

A downgraded rating of “severe” would lower the threshold on how many tons of air pollution a facility can emit before it needs a “major source” permit. A facility would have to show it was reducing more air pollution than it was adding before it could obtain such a permit, Ukeiley explained.

The environmental groups argue the Biden administration has little excuse for the delay because it’s neither a complicated nor time-consuming process to compare values from an air quality monitor to ozone benchmarks.

“The EPA’s failure to complete a simple task like downgrading the smog rating delays protection for almost 50 million people against this toxic threat,” said Kaya Allan Sugerman of co-plaintiff Center for Environmental Health in a statement. “The ambient monitoring data shows these areas clearly have dangerous levels of smog that need to be addressed as quickly as possible.”

The groups seek s a court order requiring EPA Administrator Michael Regan to issue decisions on the eight regions’ air-quality ratings.

The plaintiffs are represented by attorney Hollin Kretzmann of the Center for Biological Diversity.

Environmental Integrity Project is also a plaintiff in the lawsuit.

The EPA did not immediately respond to an email requesting comment Thursday.