In a civil action or administrative proceeding brought pursuant to Section 1102.5, once it has been demonstrated by a preponderance of the evidence that an activity proscribed by Section 1102.5 was a contributing factor in the alleged prohibited action against the employee, the employer shall have the burden of proof to demonstrate by clear and convincing evidence that the alleged action would have occurred for legitimate, independent reasons even if the employee had not engaged in activities protected by Section 1102.5.