It is true that in an at will workplace, an employee can be fired for any reason or for no reason at all so long as it is not discriminatory based on race, sex, religion, age or disability. If you were a victim of discrimination based on one of these factors, you do have a claim against the employer.
Your best avenue is to file a complaint against the company with the EEOC (www.eeoc.gov). You can find the nearest office and contact information at the website. This is a great federal agency that helps employees fight discrimination in the workplace. Their staff workers and attorneys will help you make your case against the employer.
Lawyer
Litigation Attorney