In most situations, you can fire employees for any reason at any time. This is due to at-will employment, which is any situation where you do not give your employees a contract that states terms of the employment, including termination. Most often wrongful termination lawsuits will arise due to firing a contract employee.
Cornell Law School explains wrongful termination is when you fire an employee in violation of the law. If you have a contract with your employee that states specific reasons why you may let that employee go or it includes a date for the termination of employment and you do not honor those conditions, then you break contract law.
However, you do not always have to have a written contract for an employee to claim there was a contract for employment and you violated it. An employee could prove an implied contract. In addition, it is possible for an employee to claim wrongful termination based on discrimination. You cannot use a person’s protected characteristics as a reason to fire him or her.
Another possible situation is a claim that you terminated the employee as retaliation. This might be in retaliation for reporting you to authorities for a safety issue or under whistleblower protections.
The burden of proof often lies with the plaintiff in a wrongful termination case because he or she will have to prove that you broke a law or otherwise did something illegal when terminating him or her. You will also have to provide justification for why you terminated the person’s employment to prove your defense.