It is widely established that social media afford social movement (SM) organizations new ways of organizing. Critical studies point out, however, that social media use may also trigger negative repercussions due to the commercial interests that are designed into these technologies. Yet empirical evidence about these matters is scarce. In this article, we investigate how social media algorithms influence activists’ actualization of collective affordances. Empirically, we build on an ethnographic study of two SM organizations based in Tunisia. The contributions of this paper are twofold. Firstly, we provide a theoretical framework that specifies how algorithms condition the actualization of three collective affordances (interlinking, assembling, augmenting). Specifically, we show how these affordances are supported by algorithmic facilitation, that is, operations pertaining to the sorting of interactions and actors, the filtering of information, and the ranking and aggregation of content. Secondly, we extend the understanding of how social media platforms’ profit-orientation undermines collective action. Namely, we identify how algorithms introduce constraints for organizing processes, manifested as algorithmic distortion, that is, information overload, opacity, and disinformation. We conclude by discussing the detrimental implications of social media algorithms for organizing and civic engagement, as activists are often unaware of the interests of social media-owning corporations.