Article 44 Vienna Convention on Consular Relations
Liability to give evidence
1.Members of a consular post may be called upon to attend as witnesses in the course of judicial or administrative proceedings. A consular employee or a member of the service staff shall not, except in the cases mentioned in paragraph 3 of this article, decline to give evidence. If a consular officer should decline to do so, no coercive measure or penalty may be applied to him.
2.The authority requiring the evidence of a consular officer shall avoid interference with the performance of his functions. It may, when possible, take such evidence at his residence or at the consular post or accept a statement from him in writing.
3.Members of a consular post are under no obligation to give evidence concerning matters connected with the exercise of their functions or to produce official correspondence and documents relating thereto. They are also entitled to decline to give evidence as expert witnesses with regard to the law of the sending State.
See also: Article 43 Vienna Convention on Consular Relations