Appellants are a group of individuals and employers residing in states that did not establish Exchanges. For reasons we explain more fully below, the IRS’s interpretation of section 36B makes them subject to certain penalties under the ACA that they would rather not face. Believing that the IRS’s interpretation is inconsistent with section 36B, appellants challenge the regulation under the Administrative Procedure Act (APA), alleging that it is not “in accordance with law.” 5 U.S.C. § 706(2)(A).

….Because we conclude that the ACA unambiguously restricts the section 36B subsidy to insurance purchased on Exchanges “established by the State,” we
reverse the district court and vacate the IRS’s regulation.