"Restrictions on travel and remittances to Cuba have constituted a key and often contentious component in U.S. efforts to isolate Cuba's communist government since the early 1960s. Such restrictions are part of the Cuban Assets Control Regulations (CACR), the overall embargo regulations administered by the Treasury Department's Office of Foreign Assets Control (OFAC). Various Administrations, including the current one, have eased and tightened the restrictions over the years as U.S. policy toward Cuba has changed."
CRS Report for Congress, RL31139
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html