This paper examines the spillover effect of environmental regulatory pressure on firms' green technological innovation, from the perspective of supply chain relationships. Analyzing data from Chinese listed companies, we find that the average environmental regulatory pressure faced by the customer firms of a supplier firm enhances the green patent applications filed by the supplier firm. When the industry of the supplier is more competitive or the proportion of the supplier's sales from its largest customer is higher, the supplier feels more pressured to pursue green innovation, resulting in more green patent filings. Thus, via their negotiation power, customer firms can prompt the supplier firm to innovate to meet their demand for green technologies. Finally, we show that this effect is particularly pronounced when the supplier firm has a strong financial position, is located in a highly marketized region, receives low R&D government subsidies, or enjoys a high ESG rating.

Major customers in strong bargaining position can exert pressure on dependent suppliers and adversely affect their financing conditions. Consistent with this prediction, our analysis shows that the concentration of customer bases can enhance the bargaining power of downstream customers in supplier-customer interactions, leading to the significant deterioration of financing constraints for upstream firms. We then introduce a novel machine-learning approach to analyze the heterogeneous effect of customer concentration. This allows us to identify approximately 15 % of the firms, especially those small non-SOEs, as most vulnerable to customer concentration as the bargaining effect dominates.