The proportionality of provisional measures in ICSID arbitration

International Centre for the Settlement of Investment Disputes (ICSID) tribunals increasingly regard proportionality as a requirement for the indication of provisional measures. While proportionality's relevance to the application of substantive investment protection standards has received significant scholarly attention, less discussed is proportionality's potential impact in the provisional measures context. In light of proposals raised in the ongoing ICSID Rules Amendment Project to codify a requirement of proportionality for provisional measures, this article analyses how proportionality might be used to address State concerns regarding the effect of provisional measures on their sovereign prerogatives. It argues that the proportionality requirement's codification could meaningfully alter the approach of ICSID tribunals to provisional measures in a way which is valuable to States, but which remains fair to investors. To do so, this article outlines specifically what is meant by the ‘proportionality requirement’ in the context of the ICSID provisional measures framework, as well as the concerns which have animated State comments regarding its proposed codification in the ICSID Rules (Section 2). This article then contends that the proposed codification has the potential to meet State concerns at little cost to investors (Section 3). In order to illustrate the point, ICSID tribunals’ treatment of requests for the suspension of domestic tax enforcement is contrasted against their treatment of requests for the suspension of criminal investigations or proceedings.