Trading with the Enemy
In plain English, it's not illegal for U.S. citizens to visit Cuba, but it is illegal for U.S. citizens to spend any amount of money there, in any currency. Shortly after Castro took power in 1959, the United States implemented a set of regulations designed to financially strangle the regime. Called the Cuban Assets Control Regulations, these restrictions were drawn up under the 1917 Trading with the Enemy Act and "severely restrict" travel to the island and forbid all trade. These regulations apply whether an American travels directly from the United States or via a third country. The Treasury Department, specifically OFAC, is in charge of enforcing this economic embargo. There are exceptions to the embargo, and Americans traveling under a legal license are allowed to spend a set daily amount. Licenses are available from OFAC for some journalists, diplomats, politicians, academics, athletes, art collectors, humanitarian groups, and students. In addition, Cuban Americans are allowed an annual trip to the island to visit relatives.