The term “employment” shall not include service with respect to which unemployment compensation is payable under an unemployment compensation system established by an Act of Congress; provided that the Director is hereby authorized to enter into agreements with the proper agencies under such Act of Congress, which shall become effective ten days after the date of such agreement, to provide reciprocal treatment to individuals who have, after acquiring potential rights to benefits under this Act, acquired rights to unemployment compensation under such Act of Congress or who have, after acquiring potential rights to unemployment compensation under such Act of Congress, acquired rights to benefits under this Act.