There are only a few reasons that at-will workers in the private sector can't be fired (or disciplined). Often, if you are fired for one of these reasons, a court case is too expensive and may be hard to prove.
1. You have an employment contract which gives you rights, like needing a good reason for discipline or guaranteeing your job if you don’t mess up. It can be a contract that you were given when you were hired, a letter from your company that says how long you will work, or promises in the employee handbook (although usually handbooks say that you are “at will” and the rules can be changed whenever the boss wants to). Most workers don’t have an employment contract. Usually, employment contracts are with top executives – the same folks who say we don’t need a union contract!
This is one of the most basic reasons that workers build unions. A union contract spells out how and why you can be fired and what rights you have. Union members should contact a shop steward immediately if you may be disciplined.
2. Firing you “violates public policy” or you are a whistleblower. If you were fired because you refused to break the law, it might be worth talking to a lawyer. Public policies are things which the government wants to encourage (like jury duty, not breaking government regulations and laws, etc). “Public policy” protections are different in each state, and the facts of your situation are important in determining if you have a case. If you report on something illegal that your company is doing, you may have protection. Before you do anything, read more about whistleblowing in the Resource Box on this page.
3. Retaliation for using your legally protected rights – many laws say that you can’t be fired for filing a claim or complaint under them, including workers’ comp, discrimination, OSHA, NLRA (union organizing and collective action), and FLSA (wage payment and hours of work).
Act quickly -- sometimes you have as little as 30 days to appeal when you are fired for retaliation.
4. Illegal discrimination - you are fired because you are in a protected group. Federal laws say bosses can’t discriminate against workers because of race, sex, religion, disability, age, or what country you're from. Some states have protections for these and other groups, too. Even workers who are in one of these groups may not be able to prove that they were fired because of it. For example, your boss can still fire you unfairly – he just can’t fire you because (for example) you are black, latino, a woman, 55 years old, or a person with a disability.
If you think you are being disciplined or fired because of one of these reasons, you will probably have to talk to a lawyer.