minimum standard of treatment

The minimum standard of treatment (MST) is a doctrine of customary international law requiring host states to treat foreign nationals and their property in accordance with a baseline standard of justice and protection, regardless of how the state treats its own citizens. The concept emerged in the late 19th and early 20th centuries through diplomatic protection claims, mixed claims commissions, and arbitral awards, most famously the Neer claim (US-Mexico General Claims Commission, 1926), which held that state conduct must not amount to "an outrage, to bad faith, to wilful neglect of duty, or to an insufficiency of governmental action so far short of international standards that every reasonable and impartial man would readily recognize its insufficiency."

MST stands in contrast to the national treatment standard advocated historically by Latin American states under the Calvo Doctrine, which held that foreigners are entitled only to the same treatment as nationals. The capital-exporting states (US, UK, European powers) insisted that customary international law imposes an independent floor.

Today MST is most often invoked in investment treaty arbitration. NAFTA Article 1105(1) required parties to accord investments "treatment in accordance with international law, including fair and equitable treatment and full protection and security." After divergent tribunal interpretations, the NAFTA Free Trade Commission issued a binding 2001 interpretive note clarifying that Article 1105 prescribes the customary international law minimum standard and does not require treatment beyond it. USMCA Article 14.6 (2020) carries this forward explicitly.

Typical MST obligations include:

• Denial of justice protections (access to courts, due process)
• Fair and equitable treatment (FET), where linked to MST
• Full protection and security (physical and, per some tribunals, legal security)
• Protection against arbitrary or discriminatory measures

The scope remains contested: some tribunals (e.g., Glamis Gold v. United States, 2009) read MST narrowly along Neer lines, while others (e.g., Mondev v. United States, 2002) argue the standard has evolved with state practice since 1926.