Climate change mitigation policies often impose concentrated costs in exchange for diffuse future benefits. They can ignite intense political debate, as the short-term costs associated with decarbonization disproportionately impact specific industries and communities, such as agriculture, energy, and working-class households. The associated burden has spurred opposition from stakeholders and a prominent backlash from populist parties, which politicize green policies as elitist impositions on everyday citizens. This raises the question whether mainstream political actors may react to the electoral pressure from populist parties and become less supportive of green policies. While the theoretical argument is compelling, it is not as easy to provide systematic evidence for such an effect. To do so, we make use of the fact that Members of the European Parliament (MEPs) from different countries, with varying trajectories of populist parties’ popularity, vote on the same proposals. Drawing on roll-call votes that deal with salient EU environmental legislation as identified by environmental NGOs, we use an extended spatial model of parliamentary voting to analyze the reactions of individual MEPs. The findings suggest that while populist actors politicize environmental issues, mainstream MEPs may respond by consolidating their pro-environment stances, potentially to attract centrist or left-leaning voters concerned with climate action. Our results also challenge the assertion that mainstream parties have assumed pro-mitigation policies across the board. The study contributes to the broader literature on climate policy and the politicization of environmental issues, offering a valuable perspective on the interplay between populist forces and support for environmental policies.