Minor league baseball players have officially unionized, joining the Major League Baseball Players Association after an arbitrator validated the union-authorization cards and MLB recognized the MLBPA as the players' bargaining representative.

The process of unionizing unfolded at rapid speed, starting with the distribution of cards on Aug. 28 and culminating barely two weeks later in the organizing of more than 5,000 players.

The MLBPA, which previously had represented only the 1,200 players on major league teams' 40-man rosters, will now cover all players at each of the four affiliated levels.