With which countries are FCC-licensed amateur radio stations prohibited from exchanging communications?

The International Telecommunication Union (ITU) is the specialized agency of the United Nations that manages global telecommunications and radio frequency allocation. If a sovereign nation's government decides it does not want its amateur radio operators communicating with foreign stations, it must notify the ITU. When the ITU receives such a notification, member nations, including the United States via the FCC, must respect that prohibition. Therefore, US operators are forbidden from communicating with countries that have officially registered their objection with the ITU. The distractors mentioning the American Radio Relay League (ARRL) and the International Amateur Radio Union (IARU) are incorrect because these are amateur radio advocacy organizations and clubs. They do not have the legal or governmental authority to establish or enforce international communication bans.