The quota rule in employment is a legal tool to promote gender equality in professions and positions where women are underrepresented. An accompanying assumption is that gender diversity positively affects one of the aspects of team performance in form of group cooperation. However, it is unclear whether this positive effect can be achieved if diversity increases due to a quota rule. In two fully incentivized experiments involving a real-effort task (N 1 = 188 and N 2 = 268), we examined the impact of quotas as compared to performance-based promotion on group cooperation. We thereby categorized participants either with regard to gender or to an artificial category that was randomly assigned. Cooperation within groups declined when promotion was based on quota compared to performance-based promotion, irrespective of the categorization criterion. Further analyses revealed that this negative effect of quota rules on cooperation is not driven by procedural fairness perceptions or expectations about performance of the promoted group member. Implications of the results for the implementation of equality and diversity initiatives are discussed.