15 U.S.C. § 382: Assessment of net income taxes

No State, or political subdivision thereof, shall have power to assess, after September 14, 1959 , any net income tax which was imposed by such State or political subdivision, as the case may be, for any taxable year ending on or before such date, on the income derived within such State by any person from interstate commerce, if the imposition of such tax for a taxable year ending after such date is prohibited by section 381 of this title . to invalidate the collection, on or before September 14, 1959 , of any net income tax imposed for a taxable year ending on or before such date, or to prohibit the collection, after September 14, 1959 , of any net income tax which was assessed on or before such date for a taxable year ending on or before such date.