31 CFR § 515.207 - Entry of vessels engaged in trade with Cuba.
Except as specifically authorized by the Secretary of the Treasury (or any person, agency or instrumentality designated by him), by means of regulations, rulings, instructions, licenses or otherwise,
(a) No vessel that enters a port or place in Cuba to engage in the trade of goods or the purchase or provision of services, may enter a U.S. port for the purpose of loading or unloading freight for a period of 180 days from the date the vessel departed from a port or place in Cuba; and
(b) No vessel carrying goods or passengers to or from Cuba or carrying goods in which Cuba or a Cuban national has an interest may enter a U.S. port with such goods or passengers on board.
For the waiver of the prohibitions contained in this section for vessels engaged in certain trade and travel with Cuba, see § 515.550.