Artikel 27

1. If two or more Parties have already concluded an agreement or treaty on the matters dealt with in this Convention, or have otherwise established relations on such matters, they shall also be entitled to apply that agreement or treaty or to regulate those relations accordingly, so long as they do so in a manner which is not inconsistent with the object and purpose of this Convention.
2. Parties which are members of the European Union shall, in their mutual relations, apply European Union rules governing the matters within the scope of this Convention without prejudice to the object and purpose of this Convention and without prejudice to its full application with other Parties. The same applies to other Parties to the extent that they are bound by such rules.