Organizations often hire workers whom they will not promote. We think that this practice triggers career interdependence, where hiring un- promotable workers sometimes harms but in some cases helps the mobility chances of other employees. We identify conditions that should shape such interdependence, and test our ideas by analyzing how the hiring of temporary workers affected the mobility of permanent workers in a large organization. It is expected that hiring temporary workers (1) slows permanent-worker mobility among workers at low ranks and (2) speeds mobility among advanced workers, and that these effects (3) hold for vacancy promotions but not for upgrade promotions. These hypotheses are largely supported by rate-dependent accelerated duration models estimated using event-history data on 6,850 workers over a 14-year period. The results indicate that the hiring of unpromotable workers can create a “hidden escalator” favoring core workers, and suggests the value of more research into the institutional sources of career interdependence.