28 U.S.C. § 2074

(a) The Supreme Court shall transmit to the Congress not later than May 1 of the year in which a rule prescribed under section 2072 is to become effective a copy of the proposed rule. Such rule shall take effect no earlier than December 1 of the year in which such rule is so transmitted unless otherwise provided by law. The Supreme Court may fix the extent such rule shall apply to proceedings then pending, except that the Supreme Court shall not require the application of such rule to further proceedings then pending to the extent that, in the opinion of the court in which such proceedings are pending, the application of such rule in such proceedings would not be feasible or would work injustice, in which event the former rule applies. (b) Any such rule creating, abolishing, or modifying an evidentiary privilege shall have no force or effect unless approved by Act of Congress.