Prior studies suggest that external corporate social responsibility (CSR) practices could lead to positive responses from employees, but little attention has been paid to its potential negative impacts on employees' responses. To have a comprehensive understanding of the relationship in question, we propose that there is a S‐curve relationship between external CSR and labor productivity. Found on samples of Chinese listed firms during the period from 2011 to 2017, we have drawn some conclusions as follows. First, there is a S‐curve relationship between external CSR practices and labor productivity, with labor productivity declining at low and high levels of external CSR but increasing at moderate level of external CSR. Second, internal CSR will moderate the relationship between external CSR and labor productivity that firms affiliated with high internal CSR are more likely to perform better in terms of labor productivity than firms with low internal CSR. However, the proposed negative moderating role of government subsidy on the relationship in question is not supported. It is the match between government subsidy and external CSR that may predict labor productivity.