This educational guide is based on the linked primary sources. It is not a Court publication, is not affiliated with the Court, and is not legal advice.
In brief
Overview
Environmental Defense (the petitioner) argues that the agency may not adopt a new definition of “modification” that differs from the one used under prior regulations.
The petitioner’s counsel, Mr. Hungar, says the regulation language does not support interpreting a change in hours of operation as a physical change.
The agency’s interpretation could lead to increased pollution because operating the plant 24 hours a day would double emissions compared with a 12‑hour schedule.
Background and question before the Court
Justice Kennedy asked whether courts must treat as binding a legal proposition that they think is “dead wrong.”
Justice Scalia asked what would happen if a new company, not existing when the regulation was issued, sought to challenge the regulation’s conformity with the statute.
According to Justice GINSBURG, justice Ginsburg inquired whether a new company could raise a declaration of non‑applicability.
According to Justice Stevens, justice Stevens questioned whether the agency could adopt one definition of “modification” for ten years and then change it for all programs.
Justice Stevens also asked whether the statutory text requires a uniform definition of “modification” across all regulations.
What each side argues
Petitioner (Environmental Defense)
According to Petitioner, petitioner counsel Mr. Phillips stated that it would be impermissible for the agency to adopt a regulatory interpretation of “modification” that differs from the definition used under the new source regulations.
According to Mr. HUNGAR, petitioner argued that a new company could seek a determination of non‑applicability and obtain judicial review of that determination.
According to Mr. HUNGAR, petitioner’s counsel Mr. Hungar emphasized that the regulation’s language does not support interpreting a change in hours of operation as a physical change.
According to Petitioner, petitioner noted that the term “rate” is used as an annual rate in specific statutory provisions (51.166(b)(21) and (b)(23)).
Respondent (Duke Energy Corporation)
Source-limited. The record does not yet support a complete account.
What happened at oral argument
Justice Kennedy asked whether courts must follow a legal proposition they consider “dead wrong.”
According to Justice SCALIA, justice Scalia questioned the standing of a new company to challenge the regulation’s conformity with the statute.
According to Justice GINSBURG, justice Ginsburg inquired about a declaration of non‑applicability by a new company.
Justice Stevens asked whether the agency could change its definition of “modification” after ten years.
Justice Stevens also asked whether the statutory text requires a uniform definition of “modification” across all regulations.
According to Justice Kennedy, justice Kennedy wondered whether “construction” could be interpreted to include both “modification” and a new term “alteration.”
- [1] a01c8829ff5a2771717d-r1-c148bc7cb60f4a93.pdf, p. 20
- [2] a01c8829ff5a2771717d-r1-c148bc7cb60f4a93.pdf, p. 21
- [3] a01c8829ff5a2771717d-r1-c148bc7cb60f4a93.pdf, p. 22
- [4] a01c8829ff5a2771717d-r1-c148bc7cb60f4a93.pdf, p. 39
- [5] a01c8829ff5a2771717d-r1-c148bc7cb60f4a93.pdf, p. 44
- [6] a01c8829ff5a2771717d-r1-c148bc7cb60f4a93.pdf, p. 47
What the Court decided
Why it matters
Terms to know
No glossary terms are available for this guide.
Primary sources
Read the source materials on the official site or open the immutable repository copy used for this guide.
- a01c8829ff5a2771717d-r1-c148bc7cb60f4a93.pdforal argument transcript
Guide generated September 21, 2026. Automated validation accepted this version.