No, you do not have to prove that your employer actually committed fraud against the U.S. government to succeed in a retaliation case. An employee, however, has to be able to show that there was some reasonable basis to believe that the False Claims Act was being violated. Some courts have held that an employee must be able to show that he or she had an “objectively reasonable belief” that they were attempting to prevent a false claim from being sent to the U.S. government. The exact standard will likely depend on the jurisdiction that you are in, and you should consult with an experienced False Claims Act attorney to determine if you have a strong retaliation case.