5 CFR 551.704: Claimant's representative.

A claimant may designate a representative to assist in preparing or presenting a claim. The claimant must designate the representative in writing. A representative may not participate in OPM interviews unless specifically requested to do so by OPM. An agency may disallow a claimant's representative who is a Federal employee in any of the following circumstances:

(a) When the individual's activities as a representative would cause a conflict of interest or position;

(b) When the designated representative cannot be released from his or her official duties because of the priority needs of the Government; or

(c) When the release of the designated representative would give rise to unreasonable costs to the Government.