On May 13, 2020, the United States's Special Envoy for Iran, Brian Hook, wrote in the Wall Street Journal that the United States was prepared to trigger a return of all of the Joint Comprehensive Plan of Action's (JCPOA) sanctions on Iran if the UN Security Council (UNSC) did not extend its arms embargo on Tehran. Extending this arms embargo, however, is not in the interests of other member states, mainly China and Russia, and thus will serve as a major point of contention between the United States and the rest of the UNSC.
In 2015, the government in Tehran was given sanctions relief as a result of a deal with the United States, Russia, China, Germany, Britain, and France. In that agreement, Iran promised to halt its nuclear weapons development in return for more economic freedom. However, if the United Nations Security Council discovered that Iran violated the deal, a provision was made that allowed for the return of significant sanctions.
In May of 2018, the United States officially withdrew from the JCPOA after President Donald J. Trump determined that the agreement was, "the worst deal ever." It appears, however, that because the 2015 Security Council resolution still technically still names the US as a participant, Washington believes it can trigger that return of sanctions.
Upon the release of Hook's article, China's UN Mission tweeted, "U.S. failed to meet its obligations under Resolution 2231 by withdrawing from #JCPOA. It has no right to extend an arms embargo on Iran, let alone trigger snapback. Maintaining JCPOA is the only right way moving forward."
Russia's UN Ambassador Vassily Nebenzia spoke to reporters on May 12, "They are not members, they have no right to trigger. This is ridiculous."
Most likely, the United States will face an uphill battle in its quest to spark a return of sanctions. However, it has evidence on its side, as Iran has breached several central limits of the deal, including on its stocking of enriched uranium.