While scholars have researched transnational private governance for over two decades, we still know little about some of the specific political activities in which private rulemaking schemes engage. This article addresses this topic by bringing together hitherto separate literatures on private governance and interest groups. I argue that examining private governance’s instrumental power, and interest representation and lobbying specifically, complements the literature’s dominant focus on the structural and discursive power of private governance. The article makes three contributions. First, it conceptualizes private governance schemes as interest organizations by analyzing similarities and differences with traditional interest groups. Second, the article examines instrumental power empirically by assessing the participation of 48 transnational private governance schemes in the European Union’s lobby register and variation among private governance schemes in this respect. Finally, the article contributes to developing a new research agenda to continue bridging the gap between the private governance and interest group literatures.