EPA’s controversial “Once in, always in, Rule” (Once in Rule) was recently rescinded under the Congressional Review Act, a statute which gives Congress the authority to overturn agency rules if such action is taken within specified time frames after the rules is adopted. A joint resolution Congressional resolution disapproving the rule, adopted by both the Senate and the House, was signed into law by President Trump on June 20, 2025.
Sources of hazardous air pollutants (HAPs) may once again voluntarily install air control technology or adopt production limits to reclassify as “area sources” and avoid installing more expensive air pollution control technology necessary for “major sources” of HAPs. Moreover, because the rule was disapproved under the CRA, Congressional approval will now be required for a similar rule to be adopted by EPA in the future.
Clean Air Act Permitting Scheme
The Clean Air Act (Act) establishes a system of progressively more complete and comprehensive air emissions controls depending on the amount and hazardousness of a facility’s emissions. The more comprehensive, more expensive controls apply to “major sources” of HAPs, while less complex and less expensive controls apply to “area sources,” which emit less than 10 tons per year of an individual HAP and less than 25 tons per year of all HAPs. 40 CFR 63.1 (a)(1)-(3).
The “Once In, Always In” Policy
The original "once in, always in" policy by the EPA mandated that facilities classified as major sources of HAPs would remain under stringent regulations even if their emissions fell below the major source thresholds. The "once in, always in" policy was established in 1995 by EPA under Act, stating that once a facility became a major source of HAPs, it would always be classified as such, regardless of any reductions in emissions. This interpretation of the Act was not promulgated as a rule, but rather was seen by EPA as a policy required by the terms of the Act.
Changes to the Policy
When the EPA in the first Trump administration considered the “once in, always in” policy, it issued guidance in 2018 and subsequently adopted a rule in 2020 that struck the policy down as a violation of a plain, simple reading of the Clean Air Act. “Today’s memo finds that EPA had no statutory authority under the Clean Air Act to place a time limit on when a facility may be determined to be an area source, and that a plain language reading of the Act must allow facilities to be reclassified as area sources once their potential to emit hazardous air pollutants falls below the levels that define major sources.” See here. Therefore, under the first Trump administration EPA, major sources were able to voluntarily reduce compliance burdens by reclassifying as area sources through the addition of air emission control technology or restrictions on production rates such that air emissions remain below major source thresholds.
The Once in Policy Reinstituted as a Rule
Not surprisingly, the Biden EPA reversed course and the “once in, always in” concept was promulgated as regulation, undoing the effect of the prior 2020 rulemaking. The Once in Rule was finalized in the waning days of the Biden Administration to stop industries from reducing emissions to avoid the enhanced technology required of major sources. 89 Fed. Reg. 73293 (Sept. 10, 2024). “This action amends the General Provisions of 40 CFR part 63 to require sources subject to certain major source NESHAP subparts to remain subject to those NESHAP regardless of whether they reclassify to area source status.” 89 Fed. Reg. at 73298. This was the case even if the facility later voluntarily adopted innovative technology or production limits to get below the major source threshold. Id.
The Once in Rule was not unlimited, however. It only applied to sources subject to MACT standards for seven specific persistent and bio-accumulative pollutants. The seven pollutants in question are: Alkylated lead compounds, Polycyclic organic matter (POM), Mercury, Hexachlorobenzene, Polychlorinated biphenyls (PCB), 2,3,7,8-tetrachlorodibenzofurans (TCDF), and 2,3,7,8-tetrachlorodibenzo-p-dioxin.
Review of the Once in Rule
Under Section 801(d) of the CRA, any regulation submitted to Congress either less than 60 days of session in the Senate or less than 60 legislative days in the House of Representatives before Congress adjourns a session of Congress sine die, begins a new period for congressional review of that rule becomes available in the next session of Congress. That is the case with the Once in Rule, since it passed so late in the Biden Administration. The Senate resolution disapproving the rule passed on May 1, 2025, the House resolution was adopted on May 22, 2025, and the resolution was signed by the President on June 20, 2025.
Conclusion: Next Steps
Due to this Congressional action the 2020 regulation adopted under the first Trump administration remains in effect and industry will be free to explore innovative ways to extricate itself from the more complex air technology requirements of the MACT regulations. In addition, as noted above, any rule reinstating the “once in, always in” concept would first have to be authorized by Congress. This means the days of the policy as a regulatory football are likely at an end.
