Artikel 18

A Contracting State may declare that a diplomatic officer, consular agent or commissioner authorized to take evidence under Articles 15, 16 or 17, may apply to the competent authority designated by the declaring State for appropriate assistance to obtain the evidence by compulsion. The declaration may contain such conditions as the declaring State may see fit to impose.
If the authority grants the application it shall apply any measures of compulsion which are appropriate and are prescribed by its law for use in internal proceedings.