Enforce is the wrong word to use here, because while the idea may have began with the US government, formally speaking the decision to participate or not rested with each National Olympic Committee. The US, and other Western governments in general, simply persuaded (pressured) their respective NOCs into supporting their foreign policy.
Thus the USOC was addressed by Vice-President Mondale on behalf of President Carter, in his capacity as honorary President of the USOC, at its meeting on 12 April, 1980, when by a vote of 1,604 to 797 the decision was taken not to participate in the games.
Siekmann, R. C. R. "The Boycott of the 1980 Olympic games and Détente." Essays on Human Rights in the Helsinki Process. TMC Asser Instituut, The Hague Google Scholar (1985).
USOC [had] decided not to participate because the President of the United States had declared that the national security of the country was being threatened by international events.
Siekmann, Robert CR. "International sports boycotts: sport, law and politics." Introduction to International and European Sports Law. TMC Asser Press, 2012. 379-419.
That might sound incredible today (after Iraq), but in the context of the Cold War, national security (especially where Russians were involved) was widely perceived to be very compelling reason.
Therefore, the US government did not "enforce" a boycott - the International Olympic Committee did, since (as the Wikipedia page OP linked noted) it would not admit non-NOC sanctioned athletes. Because the USOC was persuaded to agree to a boycott, that excluded US athletes.
Other athletes, sanctioned by their NOC, actually did show up at the Games despite their government's official opposition - including from Puerto Rico, demonstrating that the US government could propose and influence, but did not actually enforce a boycott.