The difficulties faced by trade unions in many developed nations have been well documented. Underlying problems of declining union membership and loss of institutional power are two major challenges: the growing numbers of employees and workplaces that are non-union, and, declining instrumentality. If unions are to successfully renew, one lever of power is potential recruits: employees who would like to join a union if one were available. In this paper, we build on the union joining literature by examining,for the first time using Australian data, the predictors of unmet demand for unions in non-union workplaces; that is, people who would be willing to join a union if one were established in their workplace. Controlling for a range of personal, job and workplace characteristics, we find two significant predictors of willingness to join a union if one were available: perceived union instrumentality and a perceived lack of managerial responsiveness to employees.