The number of games between interleague rivals such as the Yankees and Mets, Cubs and White Sox, and Dodgers and Angels will be reduced under Major League Baseball's new schedule format for 2013.

Players' union head Michael Weiner said Tuesday that in most instances the rivalry games will be cut from six to either four or three. The new format was caused by next year's move of the Houston Astros to the American League, creating two 15-team circuits and the need for interleague play throughout the season.

Says Weiner: "The reduction of traditional rivalry games was a function of fairness. Whether we end off at 3 of 4 is a function of mechanics."