Most states follow "at-will" employment, meaning either the employer or employee can end the relationship at any time for any reason — or no reason at all. However, there are important exceptions that may give you a wrongful termination claim.
Discrimination: You cannot be fired because of your race, color, religion, sex, national origin, age (40+), disability, or genetic information. Federal laws (Title VII, ADA, ADEA) and state anti-discrimination laws prohibit this.
Retaliation: Firing you for exercising a legal right is illegal. This includes filing a workers' compensation claim, reporting workplace safety violations (whistleblowing), taking FMLA leave, or complaining about wage violations.
Breach of contract: If you have a written employment contract specifying the terms of employment and termination, your employer must follow those terms. Even implied contracts (from employee handbooks or verbal promises) may be enforceable in some states.
Public policy violations: Most states recognize that termination violating a clear public policy is wrongful — for example, firing someone for serving jury duty, refusing to commit an illegal act, or reporting illegal activity.
What to do: Document everything, request your personnel file, file a complaint with the EEOC (180-300 days deadline), and consult an employment attorney. Many work on contingency fees.