The existing literature documents mixed evidence toward the association between corporate social responsibility (CSR) and corporate tax planning (e.g., Davis, Guenther, Krull, & Williams, 2016; Hoi, Wu, & Zhang, 2013). In this study, I aim to identify a causal relationship between CSR and tax planning, leveraging the staggered adoptions of constituency statutes in US states, which is a plausibly exogenous shock to firms' emphasis on their social responsibility. In general, the statutes permit firm directors to consider the interests of all constituents when making business decisions, including those who benefit from firms paying their fair share of income taxes. Thus, the adoption of the statutes raises the importance of firms' social responsibility in paying income taxes. Employing a staggered difference-in-differences (DiD) method, I find that firms incorporated in states that have adopted constituency statutes exhibit significantly higher effective tax rates (ETRs) based on current tax expense. This causal relationship suggests that managers, with the legitimacy to consider the social impact of tax avoidance, become less aggressive in tax planning. I further find that the effect of adoption is stronger for financially unconstrained firms and firms in retail businesses, where the demand (cost) for tax avoidance is lower (higher). Finally, I show that my main results are driven by firms located in states with a high sense of social responsibility and firms with high levels of tax avoidance prior to the adoption. Overall, the findings in this chapter contribute to the literature by delineating a negative causal relationship between CSR and tax avoidance and identifying a positive social impact brought by the passage of constituency legislation.