Climate change mitigation policies often impose concentrated costs in exchange for diffuse future benefits. The associated burden has spurred opposition from stakeholders and a prominent backlash from populist and radical right (PRR) parties, which politicize green policies as elitist impositions on everyday citizens. This raises the question whether mainstream political actors react to the electoral pressure from the PRR and become less supportive of green policies. While the theoretical argument is compelling, it is difficult to provide a systematic test for such an effect. To do so, we make use of the unique setting of the European Union. During the 2019-2024 term, the European Commission has taken strong initiative and proposed a considerable number of ambitious proposals to mitigate climate change, most notably linked to the European Green Deal. We leverage the fact that Members of the European Parliament (MEPs) from different countries, with varying trajectories of PRR strength, cast roll-call votes on the same proposals. The study is the first to provide an in-depth analysis of the patterns of parliamentary voting by MEPs on more than 90 important votes from 19 different mitigation policy files debated during the Ninth EP. Our quantitative analyses are completed by information from eight interviews with Members of the European Parliament and parliamentary assistants. Initial results suggest that mainstream party MEPs are less supportive of mitigation policies where the PRR is stronger, but the substantive size of the relationship is relatively small.