["Abacus, EarlyView. ", "\nDespite rising expectations for firms to fulfil environmental responsibilities, there is increasing emphasis on collaborative efforts between firms and governments to tackle sustainability challenges. This study demonstrates that governments can adjust tax enforcement to motivate such collaboration. Drawing on the theoretical perspective of government–firm reciprocity and leveraging China's low‐carbon city pilot program, we examine how governments relax tax enforcement to incentivize firms’ contributions to environmental goals. Using a multi‐period difference‐in‐differences approach, we identify two temporal stages of reciprocity. First, pilot city governments, aiming to reduce carbon emissions, relax tax enforcement, thereby lowering firms’ tax burdens to stimulate environmental effort. Second, firms use the resulting financial slack to increase environmental investment and foster green innovation, which contributes to emissions reduction in pilot cities. Cross‐sectional analyses further reveal that pilot city governments are more likely to collaborate with firms with higher pollution levels, stronger governance mechanisms, and greater information transparency. These firms, benefiting from relaxed tax enforcement, are more likely to fulfil environmental responsibilities and support government targets. Additional analyses show that firms demonstrating stronger green commitments and contributing to emissions reduction subsequently receive greater government subsidies. Overall, our study offers new insights into the interplay between environmental policies, government influence on tax enforcement, and firms’ green behaviour. It highlights how governments can leverage tax enforcement as a key mechanism to initiate partnerships with firms and foster collective efforts to address sustainability challenges.\n"]