19 U.S.C. § 2111: Basic authority for trade agreements

during the 5-year period beginning on January 3, 1975 , may enter into trade agreements with foreign countries or instrumentalities thereof; and may proclaim such modification or continuance of any existing duty, such continuance of existing duty-free or excise treatment, or such additional duties, as he determines to be required or appropriate to carry out any such trade agreement. Except as provided in paragraph (2), no proclamation pursuant to subsection (a)(2) shall be made decreasing a rate of duty to a rate below 40 percent of the rate existing on January 1, 1975 . Paragraph (1) shall not apply in the case of any article for which the rate of duty existing on January 1, 1975 , is not more than 5 percent ad valorem. the rate which is 50 percent above the rate set forth in rate column numbered 2 of the Tariff Schedules of the United States as in effect on January 1, 1975 , or the rate which is 20 percent ad valorem above the rate existing on January 1, 1975 .