Scenario: an investor sues the State for compensation, claiming its investment was expropriated. But in the very same file, the investor also owes taxes, left pollution unremediated, or breached its investment commitments. May the State «strike back» inside the same arbitration with a counterclaim, or must it open a separate case? This article analyses the legal basis, admissibility conditions and international practice of ISDS counterclaims — a weapon respondent States increasingly deploy.
The legal basis of ISDS counterclaims: the consent problem
Arbitration lives on consent, and so do counterclaims. In ISDS, the «arbitration agreement» is the State’s standing offer in an investment treaty addressed to covered investors — and most treaties draft that offer one-way: only the investor sues, over breaches of the treaty’s protection standards. A State counterclaim must therefore clear two questions: (1) do the treaty and applicable procedural rules allow counterclaims — Article 46 of the ICSID Convention lets a tribunal hear ancillary claims and counterclaims arising directly out of the subject-matter of the dispute and within the parties’ consent; UNCITRAL rules likewise open the door to counterclaims within the arbitration agreement’s scope; (2) does the counterclaim fall inside that consent, or does consent extend only to investor claims?
The condition tribunals repeat is close connection: the counterclaim must arise from the same investment, the same project, the same chain of events as the principal claim — a counterclaim «wandering off» to wholly different obligations of the investor (another project, an unrelated period) is typically cut at the jurisdictional stage. Further, the source of the counterclaimed obligation matters: tribunals distinguish treaty obligations (rarely imposed on investors), host-State law obligations, and investment-contract obligations — the second and third are a State counterclaim’s most workable ground.
International practice: two cases that shaped the field
Urbaser v. Argentina is the jurisdictional landmark: the ICSID tribunal accepted to hear Argentina’s counterclaim alleging the investor violated residents’ human right to water in the concession area — the first time such a counterclaim passed the jurisdictional gate (Argentina then lost on the merits, the tribunal finding no corresponding investor obligation under international law). The lesson: the jurisdictional door is not closed — but the investor’s obligation must be established from a concrete legal source, not from a sense of fairness.
Burlington v. Ecuador shows the financial weight of a well-built counterclaim: Ecuador counterclaimed for environmental and infrastructure damage at oil blocks, won a very substantial portion, and saw it set off directly against the compensation Ecuador owed the investor. For respondent States — including Vietnam in future cases — the message is clear: a seriously prepared environmental/tax/contract counterclaim can flip the posture from «being claimed against» to «both sides owe each other», transforming the settlement dynamics of the whole case.
Strategic meaning for both sides
For the respondent State: the counterclaim must be designed from the consultation (cooling-off) phase, not patched in mid-case — evidence of the investor’s breaches (environmental inspection conclusions, finalised tax assessments, investment-contract breach records) must be complete and quantified like a standalone claim. Price the risks too: a failed counterclaim can carry costs, and a weak one dilutes the main defence. For the investor: before filing ISDS, «audit» your own compliance file in the host State (tax, environment, labour, schedule commitments) — because the claim opens a forum in which the investor, too, may end up paying; pre-filing compliance clean-up is part of ISDS strategy, not a side task.
For Vietnam specifically: Vietnam’s treaties generally follow the traditional model (claim rights granted to investors), so a State counterclaim in an ISDS case against Vietnam must pass a non-trivial jurisdictional debate — the firmest ground is where the applicable treaty/rules open the door clearly and the counterclaim anchors to the same investment project. This is a moving field of international investment law: newer-generation treaties increasingly write investor obligations and State counterclaim doors expressly — practitioners must track each specific treaty rather than assume one common answer.
Frequently asked questions
What is a counterclaim in ISDS?
A reverse claim by the respondent (usually the State) against the claimant (the investor) inside the same arbitration, instead of a separate case. Example: the State counterclaims for environmental damage or unpaid taxes arising from the very project in dispute.
Are State counterclaims always accepted by tribunals?
No. Tribunals test two layers: whether the procedural rules/treaty open the counterclaim door (e.g. ICSID Article 46), and whether the counterclaim falls within the parties’ consent and is closely connected to the principal claim. Many older treaties grant claim rights only to investors, so counterclaims face strong jurisdictional challenges.
Has any ISDS counterclaim succeeded?
Yes: in Burlington v. Ecuador, Ecuador’s environmental counterclaim succeeded in substantial part and was set off against compensation. Urbaser v. Argentina won at the jurisdictional gate for a water-rights counterclaim but lost on the merits — the two cases are the field’s main reference points.
What should investors do to avoid counterclaims when filing ISDS?
Self-audit compliance before filing: taxes, environment, labour, and commitments in the investment certificate and project contracts. An ISDS claim opens a potentially two-way forum — the investor’s own compliance weaknesses are the respondent State’s best counterclaim material.
This article has been quality-reviewed by the FLAW AI Legal Council