Why It Matters

A recent Congressional Research Service report on hazardous air pollutants regulation reveals a Congress sharply divided over how to police toxic emissions from power plants, refineries, and manufacturing facilities. The previous Biden administration's tighter pollution standards for coal and oil-fired power plants have already been repealed, and lawmakers are now advancing competing bills to either expand Environmental Protection Agency (EPA) authority over dangerous chemicals or severely curtail it.

The battle over how strictly to regulate Hazardous Air Pollutants (HAPs) carries immediate consequences for industrial compliance costs and public health. EPA identifies mercury as a neurotoxin. The current administration has signaled it will reconsider multiple standards and encourage facilities to seek compliance extensions, signaling a regulatory pullback that will reshape enforcement priorities across the power and manufacturing sectors.

Congress has taken an active interest in recent EPA rulemaking related to the regulatory impact of HAPs standards. The stakes are high: the Trump administration's rollback of the 2012 Mercury and Air Toxics Standards (MATS) rule will increase mercury and non-mercury heavy metal emissions while producing hundreds of millions of dollars in compliance cost savings for the power industry, according to EPA's own analysis. By contrast, EPA projected no effect on retail electricity prices from the repeal.

The Big Picture

The regulatory tension centers on a fundamental question about how far a facility must go to stay regulated once it is identified as a major source. In 1995, the EPA issued guidance stating that once a facility became subject to strict MACT standards (Maximum Achievable Control Technology), it remained subject to them indefinitely. In 2018, EPA withdrew the 'once-in always-in' guidance, and in 2020, EPA formalized reclassification by rule, allowing facilities to reclassify as area sources if they reduced emissions below major source thresholds.

In 2024, EPA re-imposed the "once-in, always-in" requirement specifically for sources of the seven persistent and bioaccumulative HAPs listed under Section 112(c)(6) of the Clean Air Act, including mercury and dioxins. Congress repealed that 2024 rule in 2025 via the Congressional Review Act (CRA), restoring the ability of those sources to reclassify as area sources. On February 19–20, 2026, EPA finalized the repeal of the Biden-era 2024 amendments to MATS, reinstating the original 2012 standards.

The Senate attempted to block the MATS repeal through Senate resolution S.J.Res. 188 under the Congressional Review Act, but the motion to proceed was rejected. Meanwhile, a coalition of nonprofits and states has separately petitioned for judicial review of the MATS repeal in the D.C. Circuit Court.

What's Next

In the 119th Congress, lawmakers have introduced competing legislation to address EPA's setting of standards for HAP sources. Rep. Haley M. Stevens (D-MI) introduced the PROTECT Act of 2026, which would add PFAS as a class to the HAPs list. Rep. Yvette D. Clarke (D-NY) introduced the CLOSE Act, which would add hydrogen sulfide to the HAPs list and repeal the oil and gas source aggregation exemption. On the other side, Sen. Mike Lee (R-UT) introduced the Fair Air Enforcement Act of 2025, which would repeal citizen suit provisions of the Clean Air Act with conforming amendments to Section 112.

Bottom Line

The regulatory landscape for hazardous air pollutants remains in flux as the Trump administration reverses Biden-era standards while Congress debates competing visions for EPA authority. The rollback of MATS and the repeal of the "once-in always-in" rule signal a shift toward industry flexibility, but legislative proposals to expand HAP coverage (particularly for PFAS and hydrogen sulfide) suggest ongoing congressional pressure to strengthen protections. The outcome will significantly affect both industrial compliance costs and air quality standards across the nation.

Access the Legis1 platform for comprehensive political news, data, and insights.

---

Spot something wrong? Report an issue with this article