Article 20
1. If the Tribunal finds that two or more parties are in the same interest and are therefore to be considered as one party only, and that there is no Member of the nationality of any one of these parties upon the bench, the Tribunal shall fix a time-limit within which they may jointly choose a judge ad hoc. 2. Should any party among those found by the Tribunal to be in the same interest allege the existence of a separate interest of its own or put forward any other objection, the matter shall be decided by the Tribunal, if necessary after hearing the parties.
Article 21
1. If a Member having the nationality of one of the parties is or becomes unable to sit in any phase of a case, that party is entitled to choose a judge ad hoc within a time-limit to be fixed by the Tribunal, or by the President of the Tribunal if the Tribunal is not sitting. 2.
Parties in the same interest shall be deemed not to have a Member of one of their nationalities upon the bench if every Member having one of their nationalities is or becomes unable to sit in any phase of the case. 3. If a Member having the nationality of one of the parties becomes able to sit not later than the closure of the written proceedings in that phase of the case, that Member shall resume the seat on the bench in the case.
Article 22
1. An entity other than a State may choose a judge ad hoc only if: (a) one of the other parties is a State Party and there is upon the bench a judge of its nationality or, where such party is an international organization, there is upon the bench a judge of the nationality of one of its member States or the State Party has itself chosen a judge ad hoc; or (b) there is upon the bench a judge of the nationality of the sponsoring State of one of the other parties. 2. However, an international organization or a natural or juridical person or state enterprise is not entitled to choose a judge ad hoc if there is upon the bench a judge of the nationality of one of the member States of the international organization or a judge of the nationality of the sponsoring State of such natural or juridical person or state enterprise. 3. Where an international organization is a party to a case and there is upon the bench a judge of the nationality of a member State of the organization, the other party may choose a judge ad hoc. 4. Where two or more judges on the bench are nationals of member States of the international organization concerned or of the sponsoring States of a party, the President may, after consulting the parties, request one or more of such judges to withdraw from the bench.