The suspensions of Baez and Castro, both of whom are with Double-A Harrisburg, are effective immediately.
Baez, 24, was hitting .254 with nine home runs and 28 RBIs in 101 games, while Castro, 25, had a .296 batting average with four home runs and 36 RBIs in 96 games.
Acting general manager Mike Rizzo was not available for comment.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.