No person holding any position in the classified civil service is under obligation to contribute to any political fund or to render any political service to any person or party whatsoever, and no person shall be removed, reduced in salary or grade or otherwise prejudicated for refusing to do so. No public officer, whether elected or appointed shall discharge, promote, demote or in any manner change the official rank, employment or compensation of any person under civil service, or promise or threaten to do so, for giving or withholding, or neglecting to make any contribution of money, or any other valuable thing, for any political purpose.