WildEarth Guardians, a nonprofit environmental advocacy and conservation organization based in Santa Fe, N.M., on Friday filed a lawsuit accusing seven oil and gas companies of violating the Clean Air Act at 15 fracking sites in Weld County.

In the complaint filed in U.S. District Court in Denver, WildEarth Guardians contends that Extraction Oil and Gas, Noble Energy, Crestone Resources, Great Western Operating, Mallard Exploration, PDC Energy and Bonanza Creek Energy did not acquire permits designed to regulate and reduce the emission of volatile organic compounds into the atmosphere and should therefore halt operations until the permits are legally obtained and all fines are paid.

“By developing wells and putting them into production prior to obtaining permits, these companies have avoided compliance with stringent limits on smog-forming pollution and other toxic substances,” Randall Weiner, an environmental attorney representing WildEarth Guardians, said in a news release. “We will use these seven fracking companies’ own documents to prove their violations of the Clean Air Act’s permitting requirements.”

According to WildEarth Guardians, the companies abused a loophole that allows small sources of air pollution to submit clean air permit applications within 90 days after their oil and gas wells start producing. The 15 wells in Weld County, however, emit more than 100 tons of volatile organic compounds per year, raising them to the level of ‘major sources,’ which requires the permits be approved before any construction can begin,” according to the nonprofit.

WildEarth Guardians stated that in February it alerted all seven companies of their violations, but none sought to rectify the situation or stop production.

“The oil and gas industry is willfully violating our clean air laws at a massive scale along Colorado’s Front Range,” said Jeremy Nichols, WildEarth Guardians’ Climate and Energy Program director. “We have estimated that the companies have enjoyed more than $440 million in economic benefits by avoiding the permitting process for their facilities. This situation just highlights the need for aggressive enforcement to deter future violations and set the record straight that our health, safety and environment come before oil and gas industry profits.”

By circumventing the permitting process, WildEarth Guardians said the companies ignored key regulatory practices put in place after the U.S. Environmental Protection Agency discovered that the Denver metro and northern Front Range area did not meet federal air quality standards in 2008. ”

The companies face penalties up to $99,681 per violation per day — collectively $1.3 billion — if found in violation of the Clean Air Act, according to WildEarth Guardians.

None of the companies named in the suit responded to requests for comment.