The question of how Facebook and Google make and justify decisions regarding permissible political advertising on their platforms is increasingly important. In this paper, we focus on the U.S. case and present findings from interviews with 17 former social media firm employees (n = 7) and political practitioners (n = 11). We also analyze emails (n = 45) exchanged between Facebook government and elections staffers and two campaigns, a U.S. gubernatorial (2017) and presidential campaign (2016), regarding the platform’s policies in the context of paid speech. In addressing questions about Facebook’s and Google’s processes and policies regarding paid political content, the rationales for them, and the ability of campaigns to contest decisions, this study shows how while Facebook and Google resist being arbiters of political discourse, they actively vet paid content on their platforms. These platforms differ with respect to how and what decisions they make in the context of paid speech and within each company there are active and ongoing debates among staffers about speech. These debates at times take place in consultation with political practitioners and often occur in the context of external events. Across these firms, policies regarding speech evolve through these internal debates, appeals by practitioners, and outside pressure. At the same time, both Facebook and Google make decisions in often opaque ways, according to policies that are not transparent, and without clear justifications to campaigns or the public as to how they are applied or enforced. This limits options for political practitioners to contest regulation decisions. Finally, we conclude by arguing for the need for expanded capacities for political practitioners and the public to exercise voice around the content decisions that these firms make, and for firms to create more robust institutional mechanisms for incorporating it.