Although the low level of unionization in the U.S. has been attributed to status divisions and stratification among workers, little research has addressed the mechanisms by which status complexity limits unionization potential. Our analysis of variation in prounion attitudes in a national, U.S. sample of nonunion workers suggests that corporations have tended to legitimize themselves by appealing to the occupational identities of high-status workers whereas unions have tended to legitimize themselves by appealing to the social background identities — e.g., ethnic-racial and gender identities — of low-status workers. Our findings indicate that prounion sentiment is strongest among socially diverse, low-socioeconomic status workers.