About 1 in 5 U.S. workers — 30 million people — are subject to a so-called noncompete clause as a condition of employment. These typically forbid an employee who leaves one company from starting a similar one of their own, or working for a rival firm, for periods that can range up to several years. Defended as necessary to help companies protect trade secrets and their investments in worker training, noncompetes have now spread well beyond what’s necessary for such legitimate purposes. On balance, their impact is negative for both workers and the economy more generally. A number of states — red and blue — have limited noncompetes. But what’s really needed is a uniform federal rule. The key questions are what that rule should be, and what part of the federal government can most appropriately enact it.