No person about to be appointed to any position in the service of the City shall sign or execute a resignation, dated or undated, in advance of such appointment. No person in the service of the City shall discharge, suspend, lay-off, reduce in grade or in any manner change the official rank or compensation of any person in such service, or promise or threaten to do so, for withholding or neglecting to make any contribution of money or service or any valuable thing for any political purpose. No person in the administrative service of the City shall use his official authority to influence or coerce the political action of any person or body, or to interfere with any nomination or election to public office.