On 15th August, the Bulletin of the Atomic Scientists published an article about International Emergency Economic Powers Act. It says that IEEPA is the 1977 legislation enacted to limit the president’s national emergency powers that, oddly it says, has done the exact opposite. It was passed following some of the (many) abuses of the then system by President Nixon. It says that the President has complete discretion to declare a national emergency under IEEPA, the only requirement being that the emergency be an “unusual and extraordinary” threat that emanates in whole or substantially outside of the US. What exactly constitutes “unusual” or “extraordinary,” however, is up for interpretation, and once the president declares a threat, he can investigate, regulate, or prohibit a range of transactions and economic activities with few exceptions — primarily related to humanitarian aid and education materials. In particular, the article notes that violating IEEPA is also considered a predicate offence for financial crimes, meaning that IEEPA violations can also incur money-laundering charges, which have far stiffer penalties. This was exactly what happened in several recent cases against Chinese companies that provided intermediary financial services for North Korea.
https://thebulletin.org/2018/08/where-does-trump-get-the-power-to-reimpose-sanctions/