Revealing side effects of quota rules on group cooperation Quota rule is perceived as an effective legal tool for introducing gender equality in professions and positions where women are underrepresented. Policymakers claim that gender diversity achieved through quotas has positive effects on team performance. In an experimental, fully incentivized study (N=188) we challenged this belief by testing the impact of quotas on group cooperation using a real-effort-task. We compared quota with merit based selection procedure. To test whether these results are specific for quota rules applied to gender criteria, we manipulated group characteristics: Initial assignment to lower status group and quota rule were based either on gender or on an arbitrary randomly assigned feature (i.e. color). We found that group cooperation was negatively influenced by quota rules: cooperation increased after merit-based selection but not with a quota rule. In addition, a gender quota was perceived as the most unfair procedure.