The respective literatures on corporate social responsibility (CSR) disclosure and sustainable supplier management have grown in recent years, but little scholarly attention has been paid to the link between the two. Within a framework that incorporates legitimacy and neo-institutional theories, this study investigates how CSR disclosure in small to medium-sized enterprises (SMEs) influences CSR requirements and capacity building with suppliers. Based on an empirical data set of 146 000 SMEs, we test our hypotheses using multiple mediation analysis. Our results indicate that SME CSR disclosure has a positive direct effect on capacity building. When the mediating role of CSR requirements is taken into account, the study reveals that the more SMEs disclose their CSR activities, the more they require CSR from their suppliers, which in turn leads to an increase in capacity building with them. The study also suggests that the SMEs that limit their CSR requirements to the application step are more likely to build capacity with their suppliers than the SMEs that impose CSR verification. Overall, this article provides unique insights for practitioners seeking to determine the circumstances in which the SME practices of sustainable supplier management unfold in practice.