The debate over transgender rights has risen in prominence in recent years, with the fight over access to public restrooms and locker rooms receiving particularly heavy public attention. The legal question at the heart of the first such lawsuit to reach the Supreme Court, however, is one not of civil rights law, but of administrative law: Should courts defer to agency interpretations of their own regulations, even when those interpretations constitute major, substantive changes to public policy via informal, non-binding pronouncements? G.G. is a transgender high school student—minors are identified by letters in sensitive cases—who argues that Gloucester (Va.) High School’s policy disallowing him from using the facilities that correspond with his preferred gender identity violates federal law (Title IX of the Education Amendments) regarding sex discrimination in education. Upon being informed of G.G.’s conflict with the Gloucester County School Board, James A. Ferg-Cadima—a civil servant in the DOE’s Office of Civil Rights (OCR)—decided to get involved. He wrote a letter purporting to interpret the relevant regulation, stating that “[w]hen a school elects to separate or treat students differently on the basis of sex in [situations like this], a school generally must treat transgender students consistent with their gender identity.” While the district court rejected this interpretation, the U.S. Court of Appeals for the Fourth Circuit deferred to the agency. The Gloucester County School Board now seeks Supreme Court review. Cato Institute, along with three respected law professors (Jonathan Adler, Richard Epstein, and Michael McConnell), has filed an amicus brief supporting that petition. We do so not because we necessarily oppose OCR’s position as a matter of policy—that’s a question for another day—but because we oppose its unconstitutional method of enacting that policy. OCR seeks to change federal law not through notice-and-comment rulemaking as required by the Administrative Procedure Act, but through an informal, unpublished letter written by a low-level bureaucrat. Current Supreme Court precedent under Auer v. Robbins, 519 U.S. 452 (1997), says that courts must give such agency interpretations of their own regulations controlling deference. But deferring in this way incentivizes agencies to write vague regulations because they can be confident that they will then be free to reinterpret them at a later date without having to go through the trouble and expense of the rulemaking process—changing the law with no notice to regulated entities or the general public. Auer deference also allows executive agencies to consolidate both legislative and judicial power by effectively rewriting regulations beyond the scope delegated by Congress and then judging for themselves whether they’ve overstepped that authority. We call on the Court to take this opportunity to overrule Auer and declare that the judiciary will no longer blindly accept self-serving agency interpretations, but make their own independent determinations based on a searching and reasoned reading of the regulations at issue. Should the Court choose not to overrule Auer, we suggest that—at minimum—it hold that only agency interpretations that have received the public scrutiny of notice-and-comment rulemaking merit judicial deference.