29 CFR §15.103

1. (a)An agent or legal representative may file a claim on behalf of a claimant.
2. (b)Representative's fees are limited to not more than 20 percent of the amount paid for a claim settled in an administrative claim, and to not more than 25 percent of a judgment or settlement award after litigation is initiated. 28 U.S.C. 2678.
3. (c)If a representative is dismissed from representing a claimant before the claim is resolved, the representative may not place a lien on the claimant's recoveries under the claim.
4. (d)Any purported representative of a minor must provide documentation that he or she is the legal agent of that minor.