26 CFR § 301.9000-3 - Testimony authorizations.
(a) Prohibition on disclosure of IRS records or information without testimony authorization. Except as provided in paragraph (b) of this section, when a request or demand for IRS records or information is made, no IRS officer, employee or contractor shall testify or disclose IRS records or information to any court, administrative agency or other authority, or to the Congress, or to a committee or subcommittee of the Congress without a testimony authorization. However, an IRS officer, employee or contractor may appear in person to advise that he or she is awaiting instructions from an authorizing official with respect to the request or demand.
(b) Exceptions. No testimony authorization is required in the following circumstances -
(2) To respond solely in writing, under the direction of the attorney or other government representative, to requests and demands in IRS matters, including, but not limited to, admissions, document production, and written interrogatories to parties;
(3) To respond to a request or demand issued to a former IRS officer, employee or contractor for expert or opinion testimony if the testimony sought from the former IRS officer, employee or contractor involves general knowledge (such as information contained in published procedures of the IRS or the IRS Office of Chief Counsel) gained while the former IRS officer, employee or contractor was employed or under contract with the IRS; or
(4) If a more specific procedure established by the Commissioner governs the disclosure of IRS records or information. These procedures include, but are not limited to, those relating to: procedures pursuant to § 601.702(d) of this chapter; Freedom of Information Act requests pursuant to 5 U.S.C. 552; Privacy Act of 1974 requests pursuant to 5 U.S.C. 552a; disclosures to state tax agencies pursuant to section 6103(d) of the Internal Revenue Code (Code); and disclosures to the United States Department of Justice pursuant to an ex parte order under section 6103(i)(1) of the Code.
(c) Disclosures of IRS records or information with or without testimony authorization must be permitted under other applicable law. Any disclosure of IRS records or information that is otherwise permissible under this section must not be prohibited under applicable law. For example, in a case in which returns and return information may be disclosed, the disclosure must be authorized under section 6103, even if any required testimony authorization is obtained. If tax convention information (as defined under section 6105) may be disclosed, in deciding whether the disclosure is authorized, the authorizing official must coordinate the disclosure with the U.S. Competent Authority.