Using plant-level pollution data from Environmental Survey and Reporting Database in China, we analyze how the government's 2007 environmental policy aiming to curb pollution from two-high industries (i.e., high-polluting and high energy-consuming) affect real firm pollution activities across the supply chain. We employ the Differences-in-Differences approach and find that following the 2007 environmental policy, firms in two-high industries that are mostly in the upstream of the supply chain indeed reduce emissions of air and water pollutions significantly (e.g., sulfur dioxide (SO2), chemical oxygen demand (COD), and wastewater). Such reductions are mainly due to higher pollution removal and the increased investments in treatment facilities that are funded by subsidized bank loans such as the China Development Bank (CDB). By contrast, following the 2007 policy, firms in the downstream of two-high industries increase their production levels without any increases in their pollution treatment facilities and capabilities, which leads to increased pollution levels such as SO2 emissions and coal consumption. Furthermore, such adverse spillover effects in downstream industries can be alleviated by CDB loans, which help finance the investments in pollution treatments for these downstream firms. Our findings about direct and unintended spillover effects of the environmental policy suggest that policymakers should carefully consider all potential impacts across the supply chain when designing the package of environmental policies to mitigate unintended adverse consequences.