Rising Investor-State Tax Arbitration Cases Threaten Fiscal Sovereignty: Here’s what the UN Convention on Tax can do

The paper examines the rising trend of tax-related ISDS cases and their threat to fiscal sovereignty, proposing that the UN Convention on Tax implement carve-out clauses and coordinated treaty reforms to ensure tax disputes are handled by tax specialists and state-to-state mechanisms rather than private investment tribunals.

• Tax-related ISDS cases have increased significantly over the last two decades, representing approximately 15% of the 1,190 publicly known treaty-based ISDS cases between 2000 and 2021. Specifically, 114 claims were filed between 2010 and 2021, compared to only 51 cases before 2009.
• ISDS mechanisms threaten fiscal sovereignty by allowing private actors to challenge national tax measures through investment protection standards, which can lead to massive financial liabilities and discourage governments from implementing legitimate tax reforms.
• Existing efforts to protect tax sovereignty via 'carve-outs' in bilateral investment treaties (BITs) are largely ineffective, succeeding in fewer than 20% of cases. This failure is attributed to 'claw-back' provisions and narrow interpretations by tribunals, such as in the Yukos case.
• To effectively curb ISDS tax cases, the UN Convention on Tax protocol should include a carve-out clause covering both direct and indirect taxes, and coordinate the reform or termination of the more than 2,500 legacy international investment agreements currently in force.
• India reformed its model BIT after facing billion-dollar awards against the state resulting from ISDS claims related to retrospective capital gains taxes in the Vodafone and Cairn disputes.

APA

Readhead, A., & Lago, J. D. R. (2026). Rising Investor-State Tax Arbitration Cases Threaten Fiscal Sovereignty: Here’s what the UN Convention on Tax can do. International Institute for Sustainable Development. https://www.iisd.org/articles/policy-analysis/rising-isds-tax-arbitration-cases-threaten-fiscal-sovereignty

Chicago

Readhead, Alexandra, and Josefina del Rosario Lago. Rising Investor-State Tax Arbitration Cases Threaten Fiscal Sovereignty: Here’s what the UN Convention on Tax can do. International Institute for Sustainable Development, 2026. https://www.iisd.org/articles/policy-analysis/rising-isds-tax-arbitration-cases-threaten-fiscal-sovereignty.

Wikipedia

{{cite report |last1=Readhead |first1=Alexandra |last2=Lago |first2=Josefina del Rosario |title=Rising Investor-State Tax Arbitration Cases Threaten Fiscal Sovereignty: Here’s what the UN Convention on Tax can do |publisher=International Institute for Sustainable Development |date=23 March 2026 |url=https://www.iisd.org/articles/policy-analysis/rising-isds-tax-arbitration-cases-threaten-fiscal-sovereignty |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{readhead2026rising, author = {Readhead, Alexandra and Lago, Josefina del Rosario}, title = {{Rising Investor-State Tax Arbitration Cases Threaten Fiscal Sovereignty: Here’s what the UN Convention on Tax can do}}, institution = {International Institute for Sustainable Development}, year = {2026}, month = mar, url = {https://www.iisd.org/articles/policy-analysis/rising-isds-tax-arbitration-cases-threaten-fiscal-sovereignty}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }