Notwithstanding any other provision of this subchapter, no monthly benefits shall be paid under this section or under section 423 of this title , for any month beginning after June 30, 1968 , to an individual who is not a citizen or national of the United States and who resides during such month in a foreign country if payments for such month to individuals residing in such country are withheld by the Treasury Department under sections 3329(a) and 3330(a) of title 31.