USC Title 22 Foreign Relations, Chpt I Department of State, Sec 92.54. Letters Rogatory through diplomatic channels are mandated for formal service in all countries that are not parties to an international process treaty. Documents must be sent through diplomatic channels adhering to strict formal diplomatic protocol. The lengthy and expensive procedures are not to be confused with the procedures of The Inter American Treaty on Letters Rogatory, which does not go through the diplomatic channel, even though these methods of service share a confusingly similar name. The following is a list of the Letters Rogatory countries. Learn more about Letters Rogatory and how it affects service of process. Ancillary Legal International Process Servers have extensive experience in the laws and procedures throughout all nations.