More often than not, a termination of employment is completely lawful and cannot be challenged in court.  Employees who are fired for legitimate reasons, such as misconduct at work, poor attendance, downsizing, etc., have no recourse to court.

Even some employees who are fired for dumb reasons, for example, so that the boss can hire a family member, or because they have a personality conflict with their boss, have no recourse in court.

The at-will employment rule means that employees are only protected from a "wrongful discharge" if their case fits into the of the exceptions described in the posts below.