Within the United States, the current sales and use tax (SUT) system is riddled with complexity, in part because of the lack of coordination between jurisdictions. One vehicle of cooperative state action is the Streamlined Sales and Use Tax Agreement (SSUTA). This study employs an in-depth qualitative analysis of three states to examine the institutional and political influences on a state's decision to adopt legislation conforming to the provisions of this interjurisdictional tax agreement, and the political strategies and tactics used by supporting and opposing interest groups. Relying on interest group theory and institutional theory, case study results indicate that governmental interest groups, rather than businesses, play an important role in the adoption of inter-jurisdictional tax policy changes. The presence of strong institutional entrepreneurs and normative pressures to adopt are also critical. These findings have significant implications for jurisdictions that seek to adopt a consolidated tax base across member states, including the SSUTA, as well as potential harmonization attempts by the European Union.