Iran's Nuclear Program and U.N. Sanctions Reimposition [Updated September 18, 2020] [open pdf - 672KB]
From the Document: "U.N. Security Council Resolution 2231 (2015), which the council adopted on July 20, 2015, implements the Joint Comprehensive Plan of Action (JCPOA) and contains other provisions concerning Iran's nuclear program, Tehran's development of missiles, and arms transfers to and from Iran. The United States has threatened to invoke the resolution's 'snapback' mechanism, which requires the Security Council to reimpose U.N. sanctions lifted pursuant to Resolution 2231 and the JCPOA. The JCPOA, finalized in July 2015 by Iran and China, France, Germany, Russia, the United Kingdom, and the United States (collectively known as the P5+1), requires Iran to implement constraints on its uranium enrichment and heavy water nuclear reactor programs, as well as allow the International Atomic Energy Agency (IAEA) to monitor Tehran's compliance with the agreement. Prior to the JCPOA, these programs caused international concern because they could both have produced fissile material for use in nuclear weapons."
CRS In Focus, IF11583
Congressional Research Service: https://crsreports.congress.gov/