The law congress HAS made and a series of presidents have clung to, which, along with its other flaws, has illegally abridged the rights of Americans to freely associate with Cubans for 46 years is sometimes called the Cuban travel ban, and sometimes the Cuban embargo, and sometimes the Trading With The Enemy Act.  But it does not prohibit travel, all other countries and some U.S. businesses ignore it as an embargo, and Cuba is not the enemy of the vast majority of people who theoretically constitute the U.S. state.
    The actual name of the law is the Cuban Assets Control Act, which makes some sense because it was enacted in the interest of a tiny group of business people and their Washington pals and partners who, after they had bullied, used, abused, and robbed Cuba blind for 60 years,  lost control of what they considered their assets to the Cuban revolution a half century ago.  To these people only, most of whom are dead, whose "assets" existed in a different Cuban state, which has also been dead for half a century, the revolution was an enemy in a business sense only. But they and their U. S. government friends passed their act and dishonestly attached it to The Trading With The Enemy Act by calling Cuba's move to socialism a "national emergency," because that's the way corrupt  people with power typically do these things.
    The Trading With The Enemy Act of 1917 was meant to control business dealings with countries with which the U.S. was actually at war.  It was amended in 1940 to include "national emergency" situations that weren't quite wars.  Then, the anger of a few people, certainly not "national" in scope, over the Cuban revolution and its determination to persist, justify itself, and defend itself successfully was labeled a "national emergency,"  travel was  curtailed, sugar trade was stopped, and by July 8, 1963, the Cuban Assets Act was fully and forcefully grafted to the Trading With The Enemy Act, under the irrelevant authority of the 1940 amendment.   When that amendment was repealed in 1977, the Cuban appendage  was allowed to outlive the amendment under which it was  lamely justified (like an artificial arm floating in mid air without a body)  for as long as one president after another extends it by regularly re-signing a lie that it is "in the national interest" to do so. 
   The U.N. regularly passes near unanimous  resolutions condemning this hypocrisy.  Rational citizens regularly refuse to regard curbing their existential right to travel to Cuba as a legitimate obligation to the state.  Rabidly anti-communist  U.S. congressmen regularly add more quirks to their Act to stop unruly citizens from defying  them.  And the code regularly grows more obnoxious warts,  such as a clause forbidding anyone from going to Cuba to expand his mind under the guise of research or journalism, and another that bars travelers from tricking their parental lawgivers (presumably by  holding them to the constitution). There are now over 160 pretentiously tangled and sometimes comical subparts included in the Cuban Assets Control Regulations (Vol. 31 of the Code of Federal Regulations, ch. V, pt. 515).
    The constant revisors, endorsers, and champions of these regulations defend their outdated and never justifiable rat's nest of quasi-legal blather in shrill and expediently incoherent terms that imply national security is at stake, the connection between these regulations and the "Trading With The Enemy Act," is contrived, tenuous, and dishonestly protracted.
   While Americans who vaguely know of this connection are allowed and helped to imagine that Fidel Castro (just one person to keep it simple) is an "enemy" because he is one of the bad guys in the comic book history of the world serialized in U.S. media, the real beefs are that (1) Cuba's successful  escape from plantation status stands as a dangerous example to other third world peoples who resent being exploited  (we ARE 5% of humanity consuming something like 25% of the world's product - much more than our share in any case), (2) Americans traveling to Cuba might see that something (maybe communism) is working there, and (3) Fidel Castro is intelligent, articulate and highly respected world wide, while U.S. presidents are often held in contempt, a fact that led to the public humiliation of George Bush I at the Rio population summit - over a decade ago, but never forgotten or forgiven.