The legislature of any State may require any instrumentality of the United States (other than an instrumentality to which section 3306(c)(6) applies), and the individuals in its employ, to make contributions to an unemployment fund under a State unemployment compensation law approved by the Secretary of Labor under section 3304 and (except as provided in section 5240 of the Revised Statutes, as amended (12 U.S.C., sec. 484), and as modified by subsection (c)), to comply otherwise with such law. The permission granted in this subsection shall apply (A) only to the extent that no discrimination is made against such instrumentality, so that if the rate of contribution is uniform upon all other persons subject to such law on account of having individuals in their employ, and upon all employees of such persons, respectively, the contributions required of such instrumentality or the individuals in its employ shall not be at a greater rate than is required of such other persons and such employees, and if the rates are determined separately for different persons or classes of persons having individuals in their employ or for different classes of employees, the determination shall be based solely upon unemployment experience and other factors bearing a direct relation to unemployment risk; (B) only if such State law makes provision for the refund of any contributions required under such law from an instrumentality of the United States or its employees for any year in the event such State is not certified by the Secretary of Labor under section 3304 with respect to such year; and (C) only if such State law makes provision for the payment of unemployment compensation to any employee of any such instrumentality of the United States in the same amount, on the same terms, and subject to the same conditions as unemployment compensation is payable to employees of other employers under the State unemployment compensation law.