European integration and transformed parliamentary opposition: Evidence from five decades of legislative politics

Abstract While European integration has transformed national parliaments, its long-term impact on conflicts between governments and opposition parties remains insufficiently understood. This study addresses that gap by analysing how Sweden’s accession to the European Union (EU) in 1995 altered the patterns of parliamentary opposition. Using longitudinal data on government proposals in the Swedish parliament, 1970–2022, we apply a difference-in-differences design to compare opposition intensity before and after accession. Our findings reveal two major transformations. First, we identify a sustained decline in opposition in internationally embedded economic and tax policies, supporting the view that the EU political system structurally depoliticises economic governance. Second, we observe a gradual but pronounced politicisation in policy areas tied to national identity and social welfare, where EU competences are limited and domestic discretion remains. We thus find that European integration reshapes parliamentary conflict by dampening opposition in economic policymaking while intensifying contestation in policy areas related to national identity and social protection. Rather than reducing opposition overall, EU membership redirects it across issue areas. Taken together, the results show that the distribution of national and supranational competences conditions parliamentary opposition. As Sweden is a most likely case of EU-induced cleavage transformation, similar dynamics are likely across other member states as well. The study advances parliamentary research by shifting attention from formal powers and debates to observable opposition behaviour over time. It also adds to theories of modern-day cleavage formation by providing evidence that European integration reduces conflict in economic policy while intensifying identity-based divides.