U.S. EPA Greenhouse Gas Endangerment Finding Rescission Rule and the Tier 4 Emissions Standards Delay Proposal
Overview
In February 2026, EPA under the Trump administration finalized and published a final rule fully rescinding the 2009 "Greenhouse Gas (GHG) Endangerment Finding," issued under the Clean Air Act (CAA). Because the Endangerment Finding served as the legal foundation for all of EPA's authority to regulate GHG emissions from vehicles and factories (including the Clean Power Plan and vehicle GHG standards), this rescission has destabilized the legal basis for federal vehicle GHG regulation. In connection with this, on May 18, 2026, EPA published a proposed amendment rule (Part 1) to delay the effective date of the "Multi-Pollutant Emissions Standards" (Tier 4 criteria pollutant standards), which had applied to passenger cars and light trucks beginning with model year 2027, by two years to model year 2029.
Enforcement Timeline
December 2009: EPA publishes the 2009 Greenhouse Gas Endangerment Finding
March 2024: EPA under the Biden administration publishes the multi-pollutant emissions final rule for passenger cars and other vehicles (model years 2027–2032)
February 2026: EPA under the Trump administration publishes the final rule rescinding the 2009 Endangerment Finding, prompting numerous legal challenges
May 18, 2026: EPA publishes a proposal to delay the effective date of the Tier 4 standards from model year 2027 to model year 2029
As of 2026: Appellate litigation over the Endangerment Finding rescission and public comment coordination on the Tier 4 delay proposal are both ongoing
Business Impact
Automakers, parts suppliers, and vehicle battery manufacturers need to revisit investment plans premised on a rapid EV shift in the North American market and re-optimize product portfolios that include internal combustion engine (ICE) and hybrid electric vehicles (HEVs). The effective nullification of the federal GHG standards and the two-year delay of the Tier 4 standards reduce near-term emissions compliance costs. However, environmental NGOs and states such as California have immediately filed suits with the federal courts of appeals seeking to invalidate the Endangerment Finding rescission, so careful judgment is warranted regarding long-term technology development strategy until a final judicial determination is reached.