5 C.F.R. § 2422.4

You must serve every petition, motion, brief, request, challenge, or written objection—as well as all supporting documentation—on all parties affected by issues raised in the filing. But the service should not include any of the following: a showing of interest; evidence supporting challenges to the validity of a showing of interest; evidence supporting objections to an election; the names of voters or attendees at an election to effectuate a merger or change in affiliation; or other evidence that would reveal the identity of an employee engaged in an election proceeding. You must submit a statement of service to the Regional Director.