Assuming, as seems to be the case, that both you and your employer were covered by Family and Medical Leave Act leave, that you followed the proper procedures, and that you did not take more leave than legally allowed, your employer must reinstate you at the end of your leave--they have no choice in the matter. A failure to allow you to return violates the law and gives rise to a legal cause of action on part. You could either file a complaint with the state Department of Labor and/or consult with an employment law attorney about possibly bringing a lawsuit.