Article 27 (2)

If a dispute has not been settled in accordance with paragraph (1) within a reasonable period of time, either party thereto may, except as otherwise provided in this Treaty or agreed in writing by the Contracting Parties, and except as concerns the application or interpretation of Article 6 or Article 19 or, for Contracting Parties listed in Annex IA, the last sentence of Article 10(1), upon written notice to the other party to the dispute submit the matter to an ad hoc tribunal under this Article.