As an at will employee you may be fired for a reason, no good reason or no reason at all other than illegal discrimination. Discrimination against you based on age, gender, race, religious beliefs etc.... may give rise to a different answer. If you do not have an employment contract or union to represent you, your recourse is limited.
You might find my Legal Guide helpful "Workplace Discrimination: A Basis for Wrongful Termination Claims"
You might find my Legal Guide helpful " What Do I Tell My Lawyer"
If you have a discrimination theory about retaliatory discharge or hostile workplace conditions you'll need a lawyer.
Check with a lawyer in your locale to discuss more of the details.
Good luck to you.
NOTE: This answer is made available by the out-of-state lawyer for educational purposes only. By using or participating in this site you understand that there is no attorney client privilege between you and the attorney responding. This site should not be used as a substitute for competent legal advice from a licensed professional attorney that practices in the subject practice discipline and with whom you have an attorney client relationship along with all the privileges that relationship provides. The law changes frequently and varies from jurisdiction to jurisdiction. The information and materials provided are general in nature, and may not apply to a specific factual or legal circumstance described in the question.