Emissions Rules Are Evolving Fast—Here’s What Non-Road Equipment Manufacturers Should Know

By Mike Schmidt, AEM Director of Industry Communications -

An ever-increasing number of engine emissions-related announcements and legislative proposals are poised to impact on the non-road equipment manufacturing industry in the not-too-distant future.

However, ongoing tensions between regulatory jurisdictions make it challenging for manufacturers to predict just how the future will play out, and many of the proposed rules are best described as being in a state of flux. It's why AEM set aside some time last month to provide an in-depth breakdown of the regulatory landscape as it relates to emissions in its most recent Member Education Webinar, entitled "The Emissions Reset: What Manufacturers Need to Know."

"So many of the emissions-related regulatory activity happening today is interrelated," said AEM Senior Director of Regulatory Affairs Jason Malcore, who moderated last month's webinar. "What we're seeing play out at the state and federal level could ultimately lead to an unharmonized regulatory environment, so it's crucial for AEM members to understand the differences between these announcements, rules, and proposals, as well as prepare for their potential impact down the line."

The California Waiver and Emissions Standards

To possess a basic understanding of emissions regulations in the United States today, manufacturers need to be aware of something called "The California Waiver."

The Clean Air Act explicitly states that U.S. states cannot set their own emissions standards for new motor vehicles and engines. One state, however, is an exception to that rule: California.

California may adopt more stringent emissions standards, provided the state is granted a waiver to do so by the U.S. EPA. Because it adopted air emissions rules prior to The Clean Air Act going into effect, California can set its own rules (with certain conditions). As part of the process, though, it must request an EPA waiver when it adopts a new emissions standard or makes significant amendments to existing standards (such as changes to criteria pollutants, greenhouse gas standards, and zero-emission vehicle mandates).

The Uncertainty Surrounding the Congressional Review Act

Passed by Congress as a means to help overturn certain federal agency actions, the Congressional Review Act (CRA) is increasingly being used as a way for incoming presidential administrations to prevent outgoing administrations from passing certain rules. Simply put, if Congress passes a CRA resolution within 60 days of its submission, it essentially nullifies a federal agency action as if it had never taken place.

In terms of how the Congress Review Act relates to engine emissions rules, a trio of CRA resolutions "disapproved" EPA's waiver approvals for regulations in California in June of 2025. The moves were significant ones, as they marked the first use of CRA on EPA waivers. The action voided the approvals and barred EPA from issuing an additional waiver for those regulations in the future.

While the CRA resolutions don't directly impact the non-road sector directly, their existence suggests a desire on the part of the federal government to prevent California from developing and implementing its own emissions standards. At question is whether EPA's waivers are considered Final Rules or simply adjudicatory orders. Ultimately, according to Malcore, a likely scenario is the three waivers "disapproved" via CRA resolutions may end up being voided (and any future rules unrelated to this specific category would still need to obtain an EPA waiver).

How It All Impacts Proposed Tier 5 Engine Emissions Rules

In February of 2026, California restarted its Tier 5 engine emissions rulemaking work following a year or so of inactivity. In doing so, the state signaled its intentions to move forward with its Tier 5-related plans despite uncertainty surrounding EPA waiver approvals.

In the winter and spring of 2025, the California Air Resources Board (CARC) paused all efforts related to its proposed Tier 5 rule and indicated the work was on indefinite hiatus. However, then in June of last year, Gov. Gavin Newsom signed Executive Order N-27-25 to move forward with the next phase of the state's clean vehicle programs, prior to the state restarting Tier 5 activity. Where things head from here is a matter of debate, as California's long-term strategy regarding EPA waivers isn't fully known.

Other Engine Emissions-Related Measures to Watch

Iowa's HF 2529 - Passed in March of 2026, this act provides for the repair of a diesel exhaust fluid system that is part of farm equipment and providing penalties. It requires OEMs to provide farmers and other "interest holders" with diagnostics information, repair procedures, embedded software and firmware, diagnostic tools, and replacement parts on the same terms and at the same prices offered to authorized dealers or repair providers in the region. Unlike most Right to Repair legislation, HF 2529 explicitly addresses emissions control systems.

Federal Cold Weather Diesel Reliability Act of 2025 - The bill attempts to respond to potential failures of diesel emissions control systems in extremely cold weather, with a particular focus on Alaska. It directs EPA to revise rules to allow manufacturers to temporarily suspend SCR inducements in certain circumstances. The bill goes beyond existing SCR guidance, issues by EPA in August of 2025. This would mandate EPA to make regulatory changes.

Federal H.R. 4117 - Introduced in June of 2025, the bill would amend Section 202 of the Clean Air Act to repeal the establishment of motor vehicle emissions and fuel standards. The bill would also change section 209 of the Clean Air Act to preempt any state from setting their own standards. Ultimately, it would legislatively eliminate the EPA's and any state's authority to regulate engine emissions.

The Takeaway

"There is a fair amount of uncertainty surrounding engine emissions rules right now, and the lack of alignment and tension between various governing bodies remains a significant challenge for our industry" explained Malcore. "We encourage our members to stay up to date on these issues and learn more about what it will take to be in compliance."

About Member Education Webinars

AEM members have exclusive access to help them stay on top of emerging issues and trends via member education webinars. Experts break down industry issues and pinpoint critical changes in the landscape to help attendees refine their company's strategy.

For more information on the upcoming series of member education webinars, contact your Account Success Advisor.