Extant explanations of inter-organizational (IO) control are based on functional assumptions of information technology (IT) at the expense of structural assumptions. By focusing on structural assumptions, this paper explains how and why the formal and material properties of portable IT shape IO control. Based on analysis of portable IT mediation between a government agency and traders for tax administration, it was found that portable IT, with the support of the IO structure, reduces IO control. This occurs because portable IT invites users to subvert its connectivity and visibility with the support of the IO structure. Portable IT and IO structures are countervailing or generative depending on contingent conditions such as legislation, shared goals, and the imperative character of technology. The paper makes three main knowledge contributions: structural tensions between portable IT and IO relations; portable IT’s structure and relation; technological, human and IO agencies. Research and practical implications are discussed.