No property or interest or proceeds shall be returned under this chapter, nor shall any payment be made or judgment awarded in respect of any property or interest vested in or transferred to any officer or agency of the United States under this chapter unless satisfactory evidence is furnished to the President or such officer or agency as he may designate, or the court, as the case may be, that the aggregate of the fees to be paid to all agents, attorneys at law or in fact, or representatives, for services rendered in connection with such return or payment or judgment does not exceed 10 per centum of the value of such property or interest or proceeds or of such payment. Any agent, attorney at law or in fact, or representative, believing that the aggregate of the fees should be in excess of such 10 per centum may in the case of any return of, or the making of any payment in respect of, such property or interest or proceeds by the President or such officer or agency as he may designate, petition the district court of the United States for the district in which he resides for an order authorizing fees in excess of 10 per centum and shall name such officer or agency as respondent. The court hearing such petition, or a court awarding any judgment in respect of any such property or interest or proceeds, as the case may be, shall approve an aggregate of fees in excess of 10 per centum of the value of such property or interest or proceeds only upon a finding that there exist special circumstances of unusual hardship which require the payment of such excess. Any person accepting any fee in excess of an amount approved hereunder, or retaining for more than thirty days any portion of a fee, accepted prior to approval hereunder, in excess of the fee as approved, shall be guilty of a violation of this chapter.