President Trump, reversing an agreement negotiated by the Obama administration, abruptly ended a deal between Major League Baseball and the Cuban Baseball Federation that had eased the path for players to compete in the United States without defecting from their country.

The Trump administration said that the deal constituted a violation of trade laws because the Cuban federation was part of the government in Havana — a departure from the previous administration’s stance.

In a letter to M.L.B.’s outside counsel, which was obtained by The New York Times, Nikole Thomas, the acting assistant director for licensing at the Office of Foreign Assets Control, outlined the U.S. government’s opposition to the deal, which stipulated that the Cuban federation would receive 25 percent of a player’s signing bonus for a minor league player and between 15 and 25 percent for a major league player.

The letter said that the O.F.A.C. had “determined that M.L.B.’s payments to the Cuban Baseball Federation are not authorized” because “a payment to the Cuban Baseball Federation is a payment to the Cuban government.”