Pub. L. 93-376, tit. V, under "exemption"
exemption
exemption Sec. 510. The provisions of this title shall not apply to— (1) any Member of the United States House of Representatives or any Senator; (2) any member of a staff of any person specified in paragraph (1) while operating within the scope of his employment; (3) any member of an Advisory Neighborhood Council; (4) any person who receives less than $500 during the calendar year as compensation for performing services relating to the influencing of legislation; or (5) any entity specified in section 1(d) of title II of the District of Columbia Income and Franchise Tax Act of 1947 (D.C. Code, sec. 47–1554(d)), no substantial part of the activities of which is carrying on propaganda, or otherwise attempting to influence legislation.