The Dartmouth men’s basketball team has voted to unionize, taking an unprecedented step toward forming the first-ever labor union for college athletes. In a campus election supervised by the National Labor Relations Board, the players voted 13-2 to join Service Employees International Union Local 560, which already represents some Dartmouth workers. The school can still appeal to the NLRB and the federal courts. That could delay negotiations over a collective bargaining agreement until long after the current members of the basketball team have graduated.