In this paper, I argue that the existence of material power imbalances in systems of discourse represents a novel concern in the literature on epistemic injustice. This epistemic injustice, which I call Platform Injustice, arises from the undue assertion of agency over the background features of a system of discourse, in order to manipulate, diminish, or magnify the vocalization and reception of speech-acts. First, I demonstrate the unprecedented nature of platform control as an epistemic wrong. Next, I identify case studies of platform injustice in modern social media. Then, I situate platform injustice within Dotson’s typology of epistemic injustices; so, I can finally, identify paths to achieving platform justice and an epistemology of liberation.