The unequal assignment of employees to low-promotability tasks (e.g., extraneous paperwork; committee work) leads to disparities in worker pay and career outcomes. We identify a key predictor of low-promotability task assignment: managers’ evaluation of their employees’ intrinsic motivation. Four studies (N = 1,651; three pre-registered) demonstrated that more people assign workers they perceive as higher (vs. lower) on intrinsic motivation to low- promotability tasks. This effect occurred among MBA students with managerial experience (Study 1) and actual managers assigning tasks between their own employees (Study 2). We propose this intrinsic motivation penalty occurs in part because people believe highly intrinsically motivated employees are more resistant to burnout and that such employees enjoy low-promotability tasks more (Study 3). An intervention aimed at helping managers identify this unequal allocation attenuated this effect: people assigning multiple low-promotability tasks together (broad bracket) versus in isolation (narrow bracket) distributed tasks more equitably (Study 4).