No person holding any office, place, position or employment subject to civil service, is under any 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 grade or salary, or otherwise prejudiced for refusing so to do. 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 so to do, for giving or withholding, or neglecting to make any contribution of money, or services, or any other valuable thing, for any political purpose.