(1) Except as provided in paragraphs (b)(2), (3), and (4) of this section, a practitioner may not charge a contingent fee for services rendered in connection with any matter before the Internal Revenue Service.

(2) A practitioner may charge a contingent fee for services rendered in connection with the Service's examination of, or challenge to -

(3) A practitioner may charge a contingent fee for services rendered in connection with a claim for credit or refund filed solely in connection with the determination of statutory interest or penalties assessed by the Internal Revenue Service.

(4) A practitioner may charge a contingent fee for services rendered in connection with any judicial proceeding arising under the Internal Revenue Code.

(1) Contingent fee is any fee that is based, in whole or in part, on whether or not a position taken on a tax return or other filing avoids challenge by the Internal Revenue Service or is sustained either by the Internal Revenue Service or in litigation. A contingent fee includes a fee that is based on a percentage of the refund reported on a return, that is based on a percentage of the taxes saved, or that otherwise depends on the specific result attained. A contingent fee also includes any fee arrangement in which the practitioner will reimburse the client for all or a portion of the client's fee in the event that a position taken on a tax return or other filing is challenged by the Internal Revenue Service or is not sustained, whether pursuant to an indemnity agreement, a guarantee, rescission rights, or any other arrangement with a similar effect.

(2) Matter before the Internal Revenue Service includes tax planning and advice, preparing or filing or assisting in preparing or filing returns or claims for refund or credit, and all matters connected with a presentation to the Internal Revenue Service or any of its officers or employees relating to a taxpayer's rights, privileges, or liabilities under laws or regulations administered by the Internal Revenue Service. Such presentations include, but are not limited to, preparing and filing documents, corresponding and communicating with the Internal Revenue Service, rendering written advice with respect to any entity, transaction, plan or arrangement, and representing a client at conferences, hearings, and meetings.