September 6, 2026 - A coalition of 25 states, led by Kentucky and West Virginia, is asking the U.S. Supreme Court to review a Biden-era Environmental Protection Agency rule that tightened federal air quality standards for fine particulate matter.

Kentucky Attorney General Russell Coleman and West Virginia Attorney General JB McCuskey are leading the challenge, which seeks to overturn a June ruling by the U.S. Court of Appeals for the D.C. Circuit that upheld the stricter standard.

The EPA finalized the rule in 2024, lowering the annual National Ambient Air Quality Standard for fine particulate matter, known as PM2.5, from 12 micrograms per cubic meter to 9 micrograms per cubic meter. The agency left the 24-hour standard unchanged at 35 micrograms per cubic meter.

PM2.5 consists of airborne particles measuring 2.5 micrometers or less in diameter. The EPA tightened the annual limit after determining that the previous standard did not provide adequate protection against health risks associated with long-term exposure.

The states and business groups challenging the rule argue that the EPA improperly revisited the standard outside the Clean Air Act's regular review process. They also contend that the regulation could make it more difficult to permit new manufacturing plants, energy projects and infrastructure in areas that struggle to meet the tighter limit.

“This regulation will shut down manufacturing and raise energy costs, while doing nothing to improve public health,” McCuskey said in announcing the Supreme Court challenge. “We are once again fighting against a regulation that will make life more expensive for Americans while destroying jobs.”

The U.S. Chamber of Commerce and several other business organizations have filed a separate petition seeking Supreme Court review of the same D.C. Circuit decision. The Chamber argues that the stricter standard could have widespread implications for manufacturing, energy production, infrastructure investment and economic development.

The dispute follows a significant change in the federal government's position on the regulation. After President Donald Trump returned to office, the EPA reversed its defense of the 2024 rule and asked the D.C. Circuit to vacate it. The appeals court rejected that request along with challenges brought by states and industry groups.

In its June 26 decision, the court concluded that the EPA had authority under the Clean Air Act to revise the standard and provided sufficient scientific justification for lowering the annual PM2.5 limit.

The court noted that the EPA's Clean Air Scientific Advisory Committee had unanimously concluded that the previous standard was not adequate to protect public health, although committee members differed over how far the limit should be lowered. The EPA ultimately selected 9 micrograms per cubic meter, within the range recommended by a majority of the committee.

When the rule was finalized, the EPA estimated that the tighter standard could prevent thousands of premature deaths and hundreds of thousands of lost workdays while producing billions of dollars in annual health benefits.

Opponents, however, argue that compliance is increasingly difficult because a substantial share of particulate pollution comes from sources outside the direct control of industrial facilities, including wildfires, road dust and construction activity.

The U.S. Chamber says more than 84% of particulate matter emissions originate from non-point sources, while industrial facilities and power plants account for approximately 16%.

Industry groups have warned that areas designated as being in “nonattainment” with the federal standard can face additional permitting and regulatory requirements, potentially complicating expansion of steel mills, power plants, factories and other major industrial facilities.

The Supreme Court has not yet agreed to hear the dispute. The petitions filed by the states and business organizations ask the justices to review whether the EPA can revise national air quality standards outside the Clean Air Act's regular five-year review cycle without conducting a new comprehensive review and whether economic costs can be considered in such circumstances.

Along with Kentucky and West Virginia, the state coalition includes Alabama, Alaska, Arkansas, Florida, Georgia, Idaho, Indiana, Iowa, Kansas, Louisiana, Mississippi, Missouri, Montana, Nebraska, North Dakota, Ohio, Oklahoma, South Carolina, South Dakota, Tennessee, Texas, Utah and Wyoming.