(a) General rule. Except as provided by paragraph (b) of this section, a return or return information (including taxpayer return information), as defined in section 6103(b) (1), (2), and (3) of the Internal Revenue Code, disclosed by the Internal Revenue Service before January 1, 1977, to an officer or employee of a Federal agency (as defined in section 6103(b)(9)) for a purpose not involving tax administration (as defined in section 6103(b)(4)) pursuant to the authority of section 6103 (or any order of the President under section 6103 or rules and regulations thereunder prescribed by the Secretary or his delegate and approved by the President) before amendment of such section by section 1202 of the Tax Reform Act of 1976 (Pub. L. 94-455, 90 Stat. 1667) may be disclosed by, or on behalf of, such officer, employee, or agency after December 31, 1976, for any purpose authorized by such section (or such order or rules and regulations) before such amendment.

(b) Exception. Notwithstanding the provisions of paragraph (a) of this section, a return or return information (including taxpayer return information) disclosed before January 1, 1977, by the Service to an officer or employee of a Federal agency for a purpose unrelated to tax administration as described in paragraph (a) may, after December 31, 1976, be disclosed by, or on behalf of, such agency, officer, or employee in an administrative or judicial proceeding only if such proceeding is one described in section 6103(i)(4) of the Code and if the requirements of section 6103(i)(4) have first been met.