As the outward manifestation of corporate ESG practices, ESG events play a crucial role in disseminating ESG concepts. However, the relationship between ESG events and external stakeholders like supply chain partners remains underexplored. Using data from the supply chain networks formed by China's A-share listed companies and unlisted companies from 2010 to 2020, and distinguishing between positive and negative news reports, this study investigates the impact of customer ESG news on supplier green transformation. We find that positive ESG news coverage promotes supplier green transformation, while negative coverage inhibits it, demonstrating an asymmetric effect of ESG events. Heterogeneity tests indicate this asymmetry is more pronounced when the customer firm has stronger foundational ESG practices, higher investor attention, and greater supply chain dependency. Furthermore, geographical and cultural differences lead to variations in this asymmetry: the green spillover effect of positive ESG news is stronger when supply chain partners are located in different cities, whereas the supply chain contamination effect of negative ESG news shows the opposite pattern. Additionally, the asymmetric impact of customer ESG news on supplier green transformation exists only when suppliers have sound financial health and operate in heavily polluting industries. Our research contributes to the existing literature on the relationship between ESG publicity and green transformation among supply chain partners in emerging markets.