(a) Generally. A practitioner may not charge an unconscionable fee for representing a client in a matter before the Internal Revenue Service.

(b) Contingent fees for return preparation. A practitioner may not charge a contingent fee for preparing an original return. A practitioner may charge a contingent fee for preparing an amended return or a claim for refund (other than a claim for refund made on an original return) if the practitioner reasonably anticipates at the time the fee arrangement is entered into that the amended return or claim will receive substantive review by the Service. A contingent fee includes a fee that is based on a percentage of the refund shown on a return or a percentage of the taxes saved, or that otherwise depends on the specific result attained.