Claiming that blacks are routinely denied promotions they deserve while less qualified whites win quick trips up the corporate ladder, a group of 11 employees has filed a class-action race discrimination suit against Merck & Co. Inc.

The workers also named their union as a defendant in the suit, claiming it played a critical role in their oppression by refusing to bring grievances on their behalf when blacks were singled out for harsher discipline or were victims of racial harassment.