With the approval of the governing body of a public agency and under such regulations as it may prescribe, employees of the public agency may authorize deductions to be made from their salaries or wages either for the payment of contributions to bona fide charitable organizations or for the payment of designated sums to a nonprofit California corporation which is compelled by its by-laws to make, and which does expend such sums solely by the making of, contributions to bona fide charitable organizations.