This article addresses the rise of private authority in contemporary global governance based on the role of global law firms in the management of a specific international regime such as international investment arbitration. The purpose of the research is to demonstrate the presence and influence of private actors in the management of agendas, topics, and global issues, which derives from them being considered as authorities of a private nature. The CIADI arbitrations related to the economic and political crisis of Argentina in the period 1999-2002 are the case study that illustrates the presence of private authority in the conduction of an international regime.