Research on corporate social responsibility (CSR) disclosure recognizes the importance of the government and examines how firms respond to government CSR regulations. However, little attention is given to how government regulations affect firms’ disclosure strategy in multiple fields of CSR. Based on institutional theory, this study proposes that mandatory CSR disclosure increases the legitimacy management cost for firms, and thus firms disclose more CSR scope to gain legitimacy and less CSR emphasis to reduce costs. Using data from Chinese A-share listed firms in 2008–2018, this study finds that mandatory CSR disclosure is positively related to CSR scope but negatively related to CSR emphasis. In addition, firm visibility strengthens the aforementioned positive and negative relations, whereas market competition weakens the relation between mandatory CSR disclosure and CSR emphasis. This study contributes to the literature on CSR disclosure and studies on organizational responses to the government mandate.