In the 1996 case Auer v. Robbins, the Supreme Court ruled that where there is any ambiguity or disagreement over what a federal regulation means, courts should defer to the interpretation favored by the agency that issued the regulation. The practical consequence of this decision has been that government agencies have had the power not just to create and enforce their own rules but also to definitively interpret them. Given the mind-boggling number of federal regulations that exist — and the exceptional breadth of behavior that they govern — the importance of this "Auer deference" cannot be overestimated. While handing the powers of all three branches of government to the bureaucracy is problematic in and of itself, a recent decision by the U.S. Court of Appeals for the Ninth Circuit further extended the deference courts show to agency rule-makers by declaring that an agency's interpretation of its own rule is authoritative even if the agency has altered its interpretation dramatically since the regulation came into effect. Under that logic, an agency could spend decades saying that its regulation governing footwear only applied to shoes — and then, without warning or consultation, unilaterally decide to extend the rule to sandals and slippers (despite explicitly saying for years that they were not covered by the regulation). Such a power to rewrite regulations through after-the-fact "reinterpretation" is incredibly tempting, freeing agencies to change the rules of the game without further legislation or congressional oversight, or even the formalized rule-making process required by the Administrative Procedure Act. Peri & Sons, a family-run farm in Nevada (one of America's largest onion producers), is caught in just such an Kafkaesque morass. In its case, the Ninth Circuit ruled that even though the Department of Labor for over five years interpreted regulations issued under the Fair Labor Standards Act to mean that employers aren't required to pay employees for the costs of moving for a job (including passport and visa applications), DOL is free to change its interpretation to now require employers to cover those costs. Cato, along with the Center for Constitutional Jurisprudence and the National Federation of Independent Business, filed a brief urging the Supreme Court to hear this case. We argue not just against the Ninth Circuit's extension of Auer to cases where the agency has reversed its position, but also that Auer itself was incorrectly decided. Granting agencies post-hoc control over their regulations' textual meaning is an abdication by the courts of their constitutional duty to zealously guard against executive encroachment on the judiciary's role as interpreters of the law. And we're not alone in questioning the wisdom of Auer; as recently as 2011, Justice Scalia criticized the ruling as being "contrary to [the] fundamental principles of separation of powers." We urge the Supreme Court to take this case and restore a modicum of the Constitution's separation and balance of powers.