Under the Bush administration, the Labor Department interpreted a piece of the Fair Labor Standards Act as exempting mortgage-loan officers from eligibility for overtime pay. The Obama Labor Department didn’t see the law the same way, however, and issued a re-interpretation. This was a worrying development for the Mortgage Bankers Association, which represents banks that relied on the original interpretation and whose interests were greatly affected by the re-interpretation, but were given neither notice nor the chance to comment on the change. The MBA thus sued the Labor Department, arguing that the re-interpretation violated the Administrative Procedure Act, the 1946 law that determined, among other things, the processes that agencies have to go through when exercising their “interpretive” and “legislative” powers—that is, when they interpret laws and when they make their own regulations. Under the APA, agencies have to give affected parties notice and the opportunity for comment when making legislative rules, but do not have to do so when they merely make interpretive rules. The MBA argued that the APA requires an agency to go through the notice-and-comment process when it changes its interpretation of a law or regulation to such a degree that it is effectively making a legislative rule. The U.S. Court of Appeals for the D.C. Circuit agreed with the MBA, and now the Supreme Court has decided to review the case. The government argues that agencies are due deference when they change the application of a law through interpretive rules—so long as they come in the form of an interpretation—and that the courts don’t get a say regarding when this action becomes a legislative rule-making. Cato disagrees with the government’s position—if there’s anything our country needs, it’s not fewer checks on the administrative state—and has filed a brief supporting the MBA, joined by the Competitive Enterprise Institute and Judicial Education Network and with former White House Counsel Boyden Gray as co-counsel. In our brief, we examine the APA’s framers’ goal of rebutting the government’s assertion of administrative power. We argue that the boundary between “interpretive” and “legislative” rules is a blurry one that should be policed by the courts. The APA’s architects assumed that the courts would play such a role; they wouldn’t have made interpretive rulemaking so procedurally easy otherwise. Scholarly sources and legislative history agree that judicial review is necessary—for example, determining when “interpretive” flip-flopping necessitates greater due-process protection—to protect those whose livelihood depends on relying on and complying with agency interpretations. In sum, our brief looks to history to make clear a few important points that only the government would dispute. In a time when more people’s lives are staked on administrative rulings than ever before, we shouldn’t weaken the APA’s due-process protections. This case boils down to the government’s desire for agencies to more easily exercise power and for the subjects of regulations to have a harder time challenging that awesome authority. We, with the APA’s framers, think it should be the other way around.