EPA Returns to Prior Approach to Major Source Reclassification
In January 2026, the U.S. Environmental Protection Agency (EPA) published a final rule restoring the original language of the 2020 Major Source to Area Source rule.[1] The amendments remove the changes adopted in 2024 that required certain sources emitting hazardous air pollutants (HAPs) to continue meeting stricter major source standards even if the source had reclassified as an area source. This action restores the regulatory text from the 2020 rule “Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act” (also known as Major MACT to Area Rule or MM2A).
This action was triggered when Congress passed and the President signed a joint resolution under the Congressional Review Act that formally disapproved the 2024 rule.[2] The joint resolution voided the 2024 rule, giving it no legal effect, and EPA has now removed the invalidated language from the regulations. The amendments became effective January 2, 2026.
Who is Affected?
This action could impact sources subject to major MACT standards under Section 112 of the Clean Air Act. Under the restored 2020 rule, sources can once again reclassify from major to area source status and be subject to less stringent area source standards regardless of which HAP regulation is at issue.
Section 112 of the Clean Air Act authorizes a regulatory structure for stationary sources of HAPs. These HAP regulations apply to major and area sources of HAP.
- “Major source” is defined as “any stationary source or group of stationary sources located within a contiguous area and under common control that emits or has the potential to emit considering controls, in the aggregate, 10 tons per year or more of any hazardous air pollutant or 25 tons per year or more of any combination of hazardous air pollutants.” 42 U.S.C. 7412(a)(1).
Major sources must meet Maximum Available Control Technology (MACT) standards.
- An “area source” is any stationary source of hazardous air pollutants that does not qualify as a major source. 42 U.S.C. 7412(a)(2).
Area source standards may be based on MACT, Generally Available Control Technology (GACT), or generally available management practices.
What This Final Action Does
- removes regulatory changes made by the 2024 rule
- restores the language from the 2020 “Major MACT to Area Source” rule
A Brief History of OIAI vs. MM2A
The EPA’s approach to allowing major sources to reclassify as area sources has shifted several times over the past few decades. Here’s how the policy has evolved.
1995: EPA Establishes “Once In, Always In” Policy
In 1995, EPA issued a memorandum creating the “Once In, Always In” policy (also known as OIAI).[3] Under this policy, once the first compliance date passed, any source classified as a major source of HAP had to permanently comply with major source standards, even if the source later limited its potential emissions below major source thresholds.
While acknowledging that the Clean Air Act did not address a deadline for a source to switch from major source to area source, EPA reasoned that “sources should not be allowed to avoid compliance with a standard after the compliance date, even through reduction in potential to emit.” Another justification for the OIAI policy was to ensure that the HAP emission reductions achieved by the MACT standards would be maintained over time.
2018: EPA Rescinds OIAI and Establishes MM2A Policy
In 2018, the EPA issued a memorandum rescinding the OIAI policy, finding the policy to be contrary to the plain language of the Clean Air Act.[4] EPA explained that the language of Section 112 of the Clean Air Act did not place any “temporal limitations on the determination of whether a source emits or has the PTE HAP in sufficient quantity to qualify as a major source.” The memorandum explained that a major source could be reclassified as an area source once it takes an enforceable limit on its potential HAP emissions below major source thresholds and reduces HAP emissions to below those thresholds. Once reclassified as an area source, a source would no longer be subject to major source requirements under Section 112 of the Clean Air Act.
2020: EPA Issues MM2A Final Rule
In 2020, the EPA issued a final rule amending the General Provisions of the HAP regulations (National Emission Standards for Hazardous Air Pollutants or NESHAP) to formalize the 2018 MM2A Policy. These amendments allowed a major source to be reclassified as an area source once it limited its potential HAP emissions to levels below the major source thresholds.
2024: EPA Reinstates Limits on Reclassification
In 2024, EPA again revised the rule’s language.[5] The 2024 amendments continued to allow major sources to reclassify to area source status. However, the amendments required certain sources to continue to comply with major source emission standards (specifically, major sources subject to a NESHAP that EPA relied on to meet its obligations for seven persistent and bioaccumulative pollutants). The amended language applied to major sources that chose to reclassify to area sources after September 10, 2024.
2025: EPA Voids 2024 Rule, Reinstates MM2A
In 2025, Congress utilized the Congressional Review Act to issue a joint resolution to overturn the 2024 amendments. Under the joint resolution, the 2024 rule no longer had any legal effect.
2026: EPA Publishes MM2A Final Rule
On January 2, 2026, EPA published a final rule in the Federal Register amending the HAP regulations to revert the language back to the 2020 MM2A text.[6] The final rule amends the HAP regulations by removing the nullified 2024 amendments, thus restoring the 2020 MM2A rule language.
[1] “Congressional Review Act Revocation of 2024 Review of Final Rule Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act,” 91 Fed. Reg. 58 (Jan. 2, 2026), available here.
[2] “Review of Final Rule Reclassification of Major Sources as Area Sources Under Section 112 of Clean Air Act,” 89 Fed. Reg. 73293 (Sep. 10, 2024), available here.
[3] “Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act,” Willian L. Wehrum, Assistant Administrator, EPA (Jan. 25, 2018), available here.
[4] “Potential to Emit for MACT Standards – Guidance on Timing Issues,” John Seitz, Director of Air Quality Planning and Standards, EPA (May 16, 1995), available here.
[5] “A joint resolution providing for congressional disapproval under chapter 8 of title 5, United States Code, of the rule submitted by the Environmental Protection Agency relating to ‘Review of Final Rule Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act,’” S.J.Res.31, Public Law 119-20 (June 20, 2025), available here.
[6] “Congressional Review Act Revocation of 2024 Review of Final Rule Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act,” 91 Fed. Reg. 58 (Jan. 2, 2026), available online here.