From the Overview: "A 2015 multilateral Iran nuclear agreement (Joint Comprehensive Plan of Action, JCPOA), provides for limits on Iran's nuclear program in exchange for sanctions relief. The accord, endorsed by U.N. Security Council Resolution 2231 (July 17, 2015), contains Annex B that provides for a ban on the transfer of arms to or from Iran until October 18, 2020. The Trump Administration, with the support of many in Congress, seeks to extend the ban in order to prevent Iran from acquiring new conventional weaponry, particularly advanced combat aircraft. However, on August 14, the U.N. Security Council, including two key potential arms suppliers of Iran--Russia and China--voted down a U.S. draft to extend the arms transfer ban. Members of the Council, including the European parties to the JCPOA, also oppose a U.S. plan to implement its longstanding threat to invoke the provision of Resolution 2231 that would snap back all U.N. sanctions on Iran--if the Council does not extend the arms transfer ban."
CRS In Focus, IF11429
Congressional Research Service: https://crsreports.congress.gov/