Chevron decision is key for multiple cases that determined the EPA’s ability to regulate on emissions, pollution, and water protection.

Among the EPA rules that the high court has upheld on Chevron grounds are measures addressing air permits for greenhouse gases, interstate ozone requirements, state water quality certifications, cooling water intake rules and Endangered Species Act (ESA) considerations in state water permit delegations, among others.

The SG's brief noted that "all relevant stare decisis considerations weigh against the radical step" of overturning the doctrine. "[Over]ruling Chevron would threaten the settled expectations of parties who have relied on agency rules or orders upheld under it," the brief warned, and would "undermine the actual integrity of the judicial process."

Several EPA cases feature in the high court's Chevron jurisprudence including Utility Air Regulatory Group v. EPA, where the court held 9-0 in 2014 that EPA is allowed to interpret "air pollutant" under the Clean Air Act in a context-appropriate way, given that the existing permitting scheme would compel EPA to regulate tens of thousands of small facilities' GHG emissions.

Though EPA overstepped its authority in trying to regulate GHGs, the court held that EPA's decision was within the boundaries of its Chevron discretion, according to the Oyez blog, a free law project from Cornell's Legal Information Institute, Justia, and Chicago-Kent College of Law.

Another Chevron case is EPA v. EME Homer City Generation, also from 2014, where the court in a 6-2 holding reinstated EPA's Cross-State Air Pollution Rule after finding EPA acted within its authority in creating the cap-and-trade program.

A third, Entergy Corp. v. Riverkeeper, Inc., was decided in 2009 and held 5-4 that EPA has discretion to use a cost-benefit analysis in setting national performance standards for cooling water intake structures.

The SG's filing also lists National Association of Home Builders v. Defenders of Wildlife, a 2007 holding that the ESA did not require EPA to apply additional criteria when evaluating a transfer of pollution control jurisdiction under the Clean Water Act; and PUD No. 1 of Jefferson County v. Washington Department of Ecology where the court ruled 7-2 in favor of Washington State's Clean Water Act certification project to impose water flow requirements to protect salmon and steelhead in 1994.

One environmentalist cites the PUD No. 1 case as a prime example of why precedent is important, noting the Biden administration last fall finalized a rule that adhered to the broader interpretation upheld by that decision, reversing a Trump-era rule that took a narrower interpretation of state water quality certification powers.

The Biden rule should be "upheld under the precedent set in the 1994 holding, but because it was based on Chevron," the outcome is murky if the court tosses the doctrine, the environmentalist notes. "This recent Biden rule and the fact that there happened to be Supreme Court authority upholding EPA's interpretation is a good example of where this problem could come up," the source says. Clean Air Act

Any decision may bring specific peril for a host of Clean Air Act regulations -- including national ambient air quality standards, hazardous air pollutant limits and motor vehicle emission rules -- should the court toss Chevron on Administrative Procedure Act (APA) grounds, according to Ryan Morris, a lawyer with Workman Nydegger.