The grievance to overturn Alex Rodriguez's 211-game suspension began Monday before arbitrator Fredric Horowitz.
The New York Yankees third baseman was wearing a business suit and accompanied by lawyers when he arrived for the session at Major League Baseball's headquarters in midtown Manhattan.
Rodriguez was suspended Aug. 5 for alleged violations of baseball's drug agreement and labor contract. Because he's a first offender under the drug program and the players' association filed a grievance to force an appeal, a suspension can't start until it is upheld by an arbitrator.
The union argues the discipline is without just cause and is excessive. If the case doesn't settle, a decision by Horowitz is expected this winter