Many organizations offer justifications for why diversity matters, that is, organizational diversity cases. We investigated their content, prevalence, and consequences for underrepresented groups. We identified the business case, an instrumental rhetoric claiming that diversity is valuable for organizational performance, and the fairness case, a noninstrumental rhetoric justifying diversity as the right thing to do. Using an algorithmic classification, Study 1 (N = 410) found that the business case is far more prevalent than the fairness case among the Fortune 500. Extending theories of social identity threat, we next predicted that the business case (vs. fairness case, or control) undermines underrepresented groups' anticipated sense of belonging to, and thus interest in joining organizations-an effect driven by social identity threat. Study 2 (N = 151) found that LGBTQ+ professionals randomly assigned to read an organization's business (vs. fairness) case anticipated lower belonging, and in turn, less attraction to said organization. Study 3 (N = 371) conceptually replicated this experiment among female (but not male) Science, Technology, Engineering, and Math (STEM) job seekers. Study 4 (N = 509) replicated these findings among STEM women, and documented the hypothesized process of social identity threat. Study 5 (N = 480) found that the business (vs. fairness and control) case similarly undermines African American students' belonging. Study 6 (N = 1,019) replicated Study 5 using a minimal manipulation, and tested these effects' generalizability to Whites. Together, these findings suggest that despite its seeming positivity, the most prevalent organizational diversity case functions as a cue of social identity threat that paradoxically undermines belonging across LGBTQ+ individuals, STEM women, and African Americans, thus hindering organizations' diversity goals. (PsycInfo Database Record (c) 2022 APA, all rights reserved).