A challenge to an arbitrator is the principal procedural mechanism for addressing doubts about a tribunal member before an award is rendered. If a challenge succeeds, the arbitrator is removed and replaced in accordance with the applicable rules. If a party waits too long, however, it may lose the right to rely on the same circumstances later, including at the set-aside or enforcement stage.
The legal basis, decision-maker and deadline depend on the applicable arbitration rules and the law of the seat. The underlying principles are nevertheless similar: arbitrators must be impartial and independent, and a challenge normally requires more than a party’s subjective dissatisfaction.
Main Grounds for Challenging an Arbitrator
Lack of independence
Independence challenges focus on relationships or interests. Examples include significant professional or financial links with a party, counsel or affiliate, material economic interests, or circumstances suggesting that the arbitrator is not sufficiently detached from the dispute or its participants.
Lack of impartiality or bias
Impartiality challenges focus on possible predisposition. Bias can be party-related, but it can also concern an issue or expected outcome. Public comments, writings, behaviour during the proceedings, prior adjudicative activity and overlapping professional roles may all become relevant depending on the facts.
Failure to possess agreed qualifications
Many arbitration laws and rules also permit a challenge if an arbitrator lacks qualifications expressly agreed by the parties, such as a particular professional background, nationality requirement or technical expertise.
The “Justifiable Doubts” Standard
The most common formulation in international commercial arbitration is whether circumstances give rise to “justifiable doubts” as to impartiality or independence. This is intended to be an objective test. The question is not whether the challenging party personally distrusts the arbitrator, but whether a reasonable and informed third person, knowing the relevant facts, would have legitimate doubts.
This does not mean that challenges can be decided mechanically. Bias is inherently difficult to measure, and the same fact may carry different weight in different contexts. A prior appointment, a published view or a professional relationship may be harmless in one case and significant in another.
Actual Bias Is Usually Not Required
Modern challenge standards generally do not require proof that an arbitrator is actually biased. Requiring proof of a person’s internal state of mind would make most challenges impossible. The more workable inquiry is whether the circumstances create an appearance of bias or a reasonable risk that the arbitrator may be influenced by considerations outside the merits of the case.
This approach reflects a broader principle of adjudication: confidence in the process matters as well as the correctness of the final decision. Arbitration depends on the parties’ acceptance of private adjudication, and an objectively justified appearance of partiality can undermine that acceptance even without evidence of deliberate misconduct.
The ICSID “Manifest Lack” Requirement
ICSID Convention arbitration uses a distinct textual standard. Article 57 allows disqualification where a fact indicates a “manifest lack” of the qualities required by Article 14(1). Older decisions sometimes treated “manifest” as imposing a very demanding threshold. In Amco Asia, for example, the standard was described in terms approaching a highly probable or quasi-certain lack of the required quality.
Later decisions moved toward an appearance-based approach. Vivendi I and Urbaser are frequently cited for formulations focusing on whether a reasonable and informed third person would perceive a real risk or appearance of lack of impartiality. Other decisions, including Suez II, used more stringent language. This history explains why the standard has generated extensive debate.
Current ICSID guidance is clearer in practical terms: the standard is objective and the subjective belief of the challenging party is insufficient. A proposal under the 2022 Rules must set out the grounds, relevant facts, law, arguments and supporting documents, and is subject to a 21-day filing period.
Procedural Deadlines Can Be Decisive
Challenge deadlines are short and should be treated as substantive risk points. Under the 2021 ICC Rules, the general deadline is 30 days. Under the 2020 LCIA Rules, it is generally 14 days. Under the UNCITRAL Arbitration Rules, it is 15 days. Under the 2022 ICSID Arbitration Rules, it is 21 days after the later of tribunal constitution or the date on which the relevant facts were first known or should have been known.
Practical point. A party investigating a potential conflict should preserve the date on which each relevant fact became known. Timeliness is often litigated before the merits of the challenge are considered.
Who Decides the Challenge?
The decision-maker varies. Under institutional rules, a challenge may be decided by the institution. Under some systems, the remaining arbitrators decide, while in certain circumstances an appointing authority or institutional chair steps in. In ICSID Convention arbitration, a challenge to one arbitrator is usually decided by the other tribunal members; the Chair of the Administrative Council decides where the remaining members cannot decide, or where the proposal concerns a sole arbitrator or a majority of the tribunal.
The identity of the decision-maker can matter because challenge standards are applied in context, not in the abstract. Institutions and tribunals may emphasise different aspects of the same factual matrix, including disclosure, the IBA Guidelines, the wording of the applicable rule, and the overall appearance created by the evidence.
What Evidence Is Most Persuasive?
A successful challenge usually does not rest on speculation. Useful evidence may include appointment histories, public statements, published articles, speeches, prior awards, professional relationships, law-firm connections, funding or financial interests, and documents showing overlap between another proceeding and the pending arbitration.
The evidence should be organised around a clear theory of prejudice or dependence. A long list of weak circumstances can be less persuasive than a smaller number of facts that point in the same direction. Where issue conflict is alleged, the challenging party should identify the exact legal or factual issue said to have been prejudged and explain why it is material to the current case.
Practical Steps Before Filing a Challenge
- Identify the applicable arbitration rules, the law of the seat and any party agreement governing challenges.
- Confirm the filing deadline and document when the relevant circumstances became known.
- Separate independence concerns from impartiality or issue-bias concerns; they may overlap but require different evidence.
- Build a chronology and collect primary evidence rather than relying on general impressions.
- Assess whether the IBA Guidelines contain an analogous situation, while recognising that they are not automatically binding.
- Explain the prejudice in concrete terms: what may influence the arbitrator and why does it matter to the dispute?
- Avoid presenting ordinary adverse procedural decisions as proof of bias without additional evidence of prejudgment.
Conclusion
Arbitrator challenges are exceptional remedies, but they are essential to the integrity of arbitration. The strongest challenges combine procedural discipline with a coherent evidentiary theory. The relevant standard is generally objective, actual bias is rarely required, and context is decisive. Parties should act quickly, distinguish the type of alleged conflict, and demonstrate why an informed third party would reasonably doubt the arbitrator’s ability to decide the case impartially and independently.
Selected authorities
- R v Sussex Justices, Ex parte McCarthy [1924] 1 KB 256.
- Amco Asia Corporation v. Indonesia, ICSID Case No. ARB/81/1, Decision on Proposal to Disqualify an Arbitrator (24 June 1982).
- Compañía de Aguas del Aconquija S.A. & Vivendi Universal v. Argentina, ICSID Case No. ARB/97/3, Decision on Challenge (3 October 2001).
- Urbaser S.A. v. Argentina, ICSID Case No. ARB/07/26, Decision on Claimants’ Proposal to Disqualify Professor Campbell McLachlan (12 August 2010).
- Suez / Vivendi / AWG v. Argentina, Decision on a Second Proposal for Disqualification (12 May 2008).
