The Trading with the Enemy Act, sometimes abbreviated as TWEA, is a United States federal law, 12 U.S.C. § 95a, enacted in 1917 to restrict trade with countries hostile to the United States.

Currently, the only nations with which trade is effectively closed by the act are North Korea and Cuba.

How's that for a description?

Seriously you should let any people who may want to travel from the US to Cuba know the implications. After all this is a forum to help people out with travel
A few things for travelers from the US to know like the Cuban Democracy Act and the Helms-Burton Act.