The U.S. Environmental Protection Agency (EPA) is offering consultation with federally recognized Indian Tribes to obtain input on the first step (“Part 1”) of the Agency’s proposed two-part action to reconsider the light-and medium-duty Tier 4 criteria pollutant standards. The EPA will undertake this reconsideration through two separate rulemakings and will offer a separate consultation opportunity for the second step (“Part 2”) in the coming months.
As the first step of this two-part action, the EPA is proposing an adjustment to the implementation timeline from model year (MY) 2027 to MY 2029. In this initial proposal, titled “Revision of Tier 4 Criteria Pollutant Standards, Part 1: Amendments to Phase-In Schedule for Light-Duty and Medium-Duty Vehicles,” the Agency would amend the phase-in schedule for Tier 4 standards for certain MY vehicles. If finalized, manufacturers would continue to comply with the current Tier 3 standards for MY 2027 and MY 2028, with Tier 4 standards phasing in beginning in MY 2029. The EPA is also proposing targeted updates to emissions testing protocols and related certification requirements.
The EPA will address potential additional updates to Tier 4 standards and related program elements in a forthcoming “Part 2” rulemaking. The Tier 4 reconsideration “Part 2” action will comprehensively reconsider the Tier 4 program, which may include changes to the Tier 4 standards, implementation dates, phase-in schedules, and test procedures.
The EPA’s timeline for the consultation and coordination period is expected to extend from May 15, 2026, to July 06, 2026, which coincides with the public comment period. Please note that all consultations must be completed prior to the end of the public comment period. The deadline to request government-to-government consultation is June 22, 2026. The EPA cannot consider requests for consultation regarding this proposal if received after this date. Any consultations for this proposal will be conducted in accordance with the EPA Policy on Consultation with Indian Tribes and the Guidance for Discussing Tribal Treaty or Similar Rights.
In addition to consultation, Tribes are invited to participate in the EPA’s virtual public hearing for this proposal, which will be held on June 2-3, 2026. The EPA, in the development of the final action, will consider all comments submitted during Tribal consultation. Tribes may also submit written comments at https://www.regulations.gov/, Docket ID No. EPA–HQ–OAR–2025–3297, any time during the open comment period following publication in the Federal Register. For additional information on this proposed rulemaking and the latest information on the public hearing, please visit https://www.epa.gov/regulationsemissions-vehicles-and-engines/revision-tier-4-criteria-pollutant-standards-part-1. Information about this consultation is also available on the EPA’s Tribal Consultation Opportunities Tracking System (TCOTS).
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