The U.S. Environmental Protection Agency will reconsider its decision to place Milwaukee, Sheboygan County and Kenosha County under a stricter ozone pollution classification, reopening a fight that pits public health advocates against state officials and business leaders. The reconsideration follows months of pressure from the Wisconsin Department of Natural Resources and regional employers who argued the tougher rules unfairly penalize local industry for smog that often drifts in from elsewhere.
EPA reclassified the Milwaukee, Sheboygan County and Kenosha County nonattainment areas from Moderate to Serious in December 2024, a designation that comes with stiffer requirements for businesses under the Clean Air Act. According to the Milwaukee Journal Sentinel, the DNR formally petitioned EPA Region 5 for reconsideration, and in a July 28 letter, the agency agreed to open a notice-and-comment rulemaking process, though it said it lacked the administrative authority to directly stay the rule because its effective date had already passed, according to the Wisconsin DNR. EPA Region 5 Administrator Anne Vogel said the reconsideration will include a public comment period, per the Journal Sentinel's report.
The DNR submitted its petition on July 16, signed by Deputy Secretary Steven Little, seeking both reconsideration and a stay of the Serious designation. State environmental agency leaders and business groups have said the stricter classification created costly, burdensome requirements that would not address the root cause of Wisconsin's failure to meet ozone standards, the newspaper reported.
Court Stay Already Shields Businesses From Tougher Rules
Even before EPA's decision to reconsider, a federal appeals court had already granted Wisconsin's request to temporarily postpone the Serious classification's stricter regulations, a stay issued in September 2025. Per the U.S. EPA, a Serious designation is triggered when three-year ozone design values reach 93 to 105 parts per billion, compared with 81 to 93 ppb for Moderate — and it lowers the Clean Air Act's major source permitting threshold for volatile organic compounds and nitrogen oxides from 100 tons per year down to 50 tons, while raising emissions offset requirements for new or expanding facilities to a 1.2-to-1 ratio, according to ALL4 Inc.
With EPA now agreeing to reconsider, the U.S. Court of Appeals for the Seventh Circuit has placed the underlying lawsuit, State of Wisconsin v. EPA, in abeyance, meaning the September 2025 stay remains in effect while the administrative review proceeds, according to Michael Best & Friedrich LLP. That temporary postponement of stricter regulations will remain in place while EPA reconsiders the classification, so regional manufacturers currently remain under Moderate nonattainment rules and are avoiding the lower 50-ton threshold for now.
Business Leaders Say Wisconsin Is Being Punished for Others' Pollution
State Sen. Dale Kooyenga said DNR's support for reconsidering the reclassification means the decision is based on science, adding that emissions reductions should be enforced where the emissions actually originate rather than falling on Wisconsin businesses. Kooyenga also said EPA is not applying the right enforcement mechanisms to the right businesses, according to the Journal Sentinel's reporting. The Metropolitan Milwaukee Association of Commerce filed an amicus brief supporting Wisconsin's challenge, arguing that a Serious classification penalizes local employers for pollution originating in upwind states like Illinois and Indiana, according to MMAC.
Ozone pollution does drift over Lake Michigan from other states, and it forms when gases from cars, power plants, chemical plants and other sources mix with sunlight and heat. U.S. Rep. Tom Tiffany, the likely Republican nominee for governor of Wisconsin, said in March that he would ask EPA to end the state's vehicle emissions testing requirement, which currently requires drivers in Kenosha, Milwaukee, Ozaukee, Racine, Sheboygan, Washington and Waukesha counties to obtain biennial inspections before renewing plates for 1996-and-newer gasoline vehicles and 2007-and-newer diesel vehicles under 14,000 pounds, according to Wisco Automotive.
Health Advocates Warn of Real Costs to Delay
Not everyone agrees the reconsideration is good news. Amy Barrilleaux said pollution controls have costs, but hospitalizations and missed work and school days also have costs, and she added that ozone is affecting people's health throughout the region regardless of where it originates. Ozone exposure is linked to sore throat, shortness of breath, coughing and headaches, and long-term exposure can produce new cases of asthma along with other respiratory issues and premature death.
The stakes are especially high in Milwaukee. According to a 2025 report from the Asthma and Allergy Foundation of America cited by University of Wisconsin-Milwaukee researchers in January, Milwaukee recorded the highest rate of asthma-related emergency department visits among all major U.S. metro areas, and Milwaukee Public School children are roughly twice as likely to have asthma as school-aged peers nationally. Wisconsin's statewide ozone concentrations have dropped more than 20% over the last two decades, but that progress has slowed in recent years, and climate change is increasing opportunities for unhealthy summertime ozone levels.
Data Center Growth Adds a New Wrinkle
Wisconsin utilities have extended coal plant operations to serve growing electricity demand, including demand tied to data centers, complicating the state's efforts to keep making progress on ozone. Hoodline previously reported that environmental groups including the Sierra Club challenged air permits for proposed AI data centers in southeastern Wisconsin, warning that backup diesel generators at facilities like a planned Port Washington campus emit significant nitrogen oxides that worsen local ozone formation.
The current fight over nonattainment boundaries is not the first. In 2020, the D.C. Circuit ruled in Clean Wisconsin v. EPA that the agency acted arbitrarily when designating several Wisconsin counties as attainment without adequate explanation, and Clean Wisconsin won that 2018 lawsuit to keep parts of the region classified as nonattainment areas, according to Justia. Nonattainment status requires stricter regulations whenever an area fails to meet federal standards, and a Serious classification would place more Wisconsin businesses under regulation while requiring larger percentage cuts in emissions.
An EPA spokesperson has not provided details about how long the reconsideration process will take or when a decision will be made. For now, the fight over who bears responsibility for southeast Wisconsin's smog — and who pays the price for it — remains unresolved.
