Conventional wisdom among scholars and news media states that Congress is a minor player in the negotiation of international treaties because it lacks power and due to informational barriers. This paper demonstrates that formal institutional rules of Brazilian decision-making process give more power to Congress than previously recognized. It shows how the Brazilian Congress worked as a veto-player only when treaties content included sensitive subjects that could threaten the national sovereign. The paper argues that the role of Congress is not restricted due to lack of information or reduced institutional power, but due to the content of the treaties. That institutional power restricts the topics advanced by the Executive during the negotiations.