Each attorney, certified public accountant, enrolled agent, or enrolled actuary who, having been retained by a client with respect to a matter administered by the Internal Revenue Service, knows that the client has not complied with the revenue laws of the United States or has made an error in or omission from any return, document, affidavit, or other paper which the client is required by the revenue laws of the United States to execute, shall advise the client promptly of the fact of such noncompliance, error, or omission.