You may have grounds for a lawsuit if you can get your hands on some very specific evidence such as memos, email messages, comments, or statistics showing that your employer has discriminatory promotion practices. This evidence is hard to come by, as most employers these days are savvy enough to keep discriminatory motives under wraps (even if they aren't savvy enough to abandon those motives altogether).

It sounds as if your employer is being close-lipped about why you didn't get the position and the law does not require employers to explain their job decisions. It doesn't necessarily mean your employer had a discriminatory motive, so you'd be wise to seek out a sympathetic ear within the company and explain that you feel stymied in your attempts to advance to another position. Try to set aside your past feelings of rejection. Avoid comments about why you feel the person they hired for the job you wanted is a bad fit. Ask instead for advice on what you might do to get ahead or move to another position you would rather have.

If this initial discussion doesn't allay your suspicions of discrimination, check your employee handbook to see if there is a process for expressing such concerns to your employer, such as a complaint procedure. You might also ask for a confidential meeting with someone in your human resources department so that you can explain your concerns and ask for some concrete answers.

If all else fails, consider filing a complaint with your local office of the Equal Employment Opportunity Commission (EEOC), the federal agency that enforces federal antidiscrimination laws, or with your state's fair employment agency. If either agency chooses to investigate your complaint, it can ask your employer to explain why it did not offer you the position that you wanted.