This article addresses a largely unchartered interdisciplinary research area of the global investment regime and European Union (EU) law with an emphasis on the prevention of international tax avoidance in the EU. It focuses on the intersections between newly proposed anti-tax avoidance legislation by the European Commission that is known as the Unshell Directive (UD) and international investment agreements (IIAs). In this article, the author sets a stage for the intersections by discussing the Court of Justice of the European Union (CJEU) case law and the commission’s actions aimed against the most powerful enforcement tool in the global investment regime, i.e., the investor-state dispute settlement (ISDS) mechanism, by attempting to render it illegal and ineffective within the EU. The corresponding reactions from the arbitral tribunals are also addressed. The discussion evolves to identify and analyse the interplay between the proposal of the UD (also the Unshell Proposal or UP) and the IIAs to reveal that the impact of the former on the latter is ambiguous by design in order to minimalize legal certainty vis-à-vis protection of foreign investment in the EU via shell entities. This constitutes a foundation for potential, seismic tensions between the UD and the global investment regime that are not beneficial for marketing and development of the EU internal (single) market and may thus weaken the EU’s global competitiveness in the area of foreign investments.