The term “employment” shall not include service performed in the employ of any other State or its political subdivisions, or of the United States Government, or of an instrumentality of any other State or States or their political subdivisions or of the United States except that, in the event that the Congress of the United States shall permit States to require any instrumentalities of the United States to make payments of contributions under a State Unemployment Compensation Act (and to comply with State regulations thereunder), then, to the extent permitted by Congress, and from and after the date as of which such permission becomes effective, all of the provisions of this Act shall be applicable to such instrumentalities and to services performed for such instrumentalities in the same manner, to the same extent, and on the same terms as to all other employers, employing units, individuals, and services; provided, that if this State shall not be certified for any year by the Secretary of Labor of the United States of America or other appropriate Federal agency under Section 3304 of the Federal Internal Revenue Code of 1954, then the payments required of such instrumentalities with respect to such year shall be refunded by the Director in accordance with the provisions of Section 2201.