There is no simple answer to this question, because many types of lawsuits fall under the general heading of "wrongful termination." The statute of limitations for your case depends on the legal claims underlying your lawsuit.
The statute of limitations is the legal time limit for filing a lawsuit based on a particular claim. If you file a lawsuit after the statute of limitations has expired, your case can be thrown out.
Statutes of limitations may be set by state or federal law.
If you are suing for discrimination under federal law, you have 180 days to file a charge of discrimination with the Equal Employment Opportunity Commission; this time limit is extended to 300 days if your state or local government has a law prohibiting the same type of discrimination. Once the EEOC issues a right to sue letter, you have 90 days to file a lawsuit.
If you are suing under a state law prohibiting discrimination, the statute of limitations may be different.
If your lawsuit is based on breach of an employment contract, the statute of limitations is set by state law. Many states have different time limits for oral contracts and written contracts; the limit for written contracts is typically longer, because the case won't rely solely on people's memories. The statute of limitations for bringing a contract case ranges from two to 15 years.
If you are suing for defamation, wrongful termination in violation of public policy, or other claims classified as "personal injury" lawsuits, state law sets the statute of limitations. In most states, the time limit is two or three years.
To find out the statute of limitations in your state for contract and tort claims, see the Nolo chart Statutes of Limitations in All 50 States.