How do opposition actors in electoral authoritarian regimes use social media to galvanize support? Based on 2,229 social media posts, I examine how Aleksey Navalny and the Communist Party (KPRF) politicize grievances about the pension reform of 2018 and use Twitter and VKontakte for protest mobilization. I find that Navalny integrates the reform in his narrative of government corruption and theft, strategically using the platforms' different advantages. The KPRF frames less coherently and makes no distinction between VKontakte and Twitter. These differences, I argue, are mainly due to actors' different target audiences and their respective position in the authoritarian political system