Social-democratic parties face a dilemma between the universalist ethos of their socialist tradition and the nationalism that they share with the other political actors of the state where they act. In this paper, we examine comparatively the position of the Spanish party Partido Socialista Obrero Español (PSOE) and the Catalan party Esquerra Republicana de Catalunya (ERC) on three political debates that pertains to the link between welfare and identity in Spain. We show how these parties experience opposite tensions between nationalism and the universalism of their left-wing ideology. Whereas ERC calls for a withdrawal from the Spanish system of social security, the PSOE advocates imposing on Catalonia a symmetric form of solidarity with the rest of Spain, despite recognising the region's different identity. Above all, both parties take identity for granted as a pre-political factor that ‘naturally’ justifies differential treatment, according to ERC, or equalising federalism, in the case of the PSOE.