IF your weight is due to a medical condition considered a "disability" (a diagnosed and defined condition which has a significant persistent effect on major life activities), then you could bring a disability-discrimination claim: the law prohibits discriminating against or harassing employees due to disabilities. However, if you do not have what would be considered a disability, you could not sue your employer: while the law protects people with disabilities, it does not protect being overweight not due to a medical disability.