Here is what the State Department says about travel to Cuba:
"The U.S. Department of the Treasury enforces the Cuban Assets Control Regulations, which apply to all U.S. citizens and permanent residents wherever they are located, all people and organizations physically located in the United States, and branches and subsidiaries of U.S. organizations throughout the world. The regulations require that persons subject to U.S. jurisdiction be licensed in order to engage in any travel-related transactions pursuant to travel to, from, and within Cuba. Transactions related to travel for tourist activities are not licensable. This restriction also prohibits tourist travel to Cuba from or through a third country such as Mexico or Canada. U.S. law enforcement authorities enforce these regulations at U.S. airports and pre-clearance facilities in third countries. Travelers who fail to comply with Department of the Treasury regulations could face civil penalties and criminal prosecution upon return to the United States."
The State Deparment also notes that "general licenses are granted to the following categories of travelers, who are permitted to spend money to travel to Cuba and to engage in other transactions directly incident to the purpose of their travel, without the need to obtain a specific license from the U.S. Department of the Treasury's Office of Foreign Assets Control," including those visiting close relatives; journalists; official government travelers on official business; religious organizations. See http://www.travel.state.gov for more exceptions.Copyright © 2014, Los Angeles Times