10 C.F.R. § 708.29

The complainant has the burden of establishing by a preponderance of the evidence that he made a disclosure, participated in a proceeding, or refused to participate, as described under § 708.5, and that such act was a contributing factor in one or more alleged acts of retaliation against the complainant by the contractor. Once the complainant has met this burden, the burden shifts to the contractor to prove by clear and convincing evidence that it would have taken the same action without the complainant's disclosure, participation, or refusal.