This article is a contribution to debates on the role of trade unions and industrial relations institutions in boosting popular support for a greener economy. Building on prior work that demonstrates a positive association between collective bargaining coverage and pro-environmental attitudes among workers, the article adds a more robust country-comparative focus. Matching data from the European Social Survey with the new European Participation Index (EPI), it examines whether cross-national variation in the strength of unions and industrial relations institutions is related to country differences in public support for carbon taxation and considers a range of explanatory factors. Results of multi-level regression models support the core argument by revealing a positive association between the EPI and public support for carbon taxation, which is robust to several control variables, including the domestic weight of the fossil fuel industry. The article thus highlights the importance of trade unions and industrial relations institutions in the successful navigation of green transitions.