The Major League Baseball Players Association formally appealed Alex Rodriguez's 211-game suspension Wednesday, sending the case to an independent arbitrator.
Union spokesman Greg Bouris confirmed the appeal and said the players' association had no further comment. A message was left seeking comment from Major League Baseball.
Rodriguez, who was back at third base and batting third for the New York Yankees against the Chicago White Sox on Wednesday night, said he had "no reaction" to the filing of the grievance.
The three-time MVP was suspended through the 2014 season on Monday when the league penalized 13 players following an investigation into Biogenesis of America, a shuttled Florida anti-aging clinic accused of distributing banned performance-enhancing drugs.
The other 12 players accepted 50-game suspensions, but Rodriguez said he planned to fight. Union head Michael Weiner said the punishment for the slugger was "way out of line."
Rodriguez's punishment was scheduled to begin Thursday, but he is allowed to keep playing until the grievance is heard by arbitrator Fredric Horowitz. He isn't expected to rule until November or December at the earliest.
Coming back from hip surgery in January, Rodriguez played his first game of the season Monday night in the series opener at Chicago. He singled in his first at-bat and was 2 for 6 with a walk in his first two games.
Rodriguez has been booed lustily since his return, except for when he was hit by a pitch in the third inning of Tuesday night's 3-2 loss.