No person, while an officer or other member of the Fire Department of the City, shall publicly endorse any candidate for political office, serve as a campaign assistant on behalf of any candidate for political office, or perform any public campaign activity on behalf of any candidate for public office for which Burlington voters are casting ballots. The foregoing shall not prohibit a fire officer from voting in any election; or from expressing his or her views concerning any referendum question being considered; and shall not prevent a collective bargaining unit which represents fire officers from endorsing candidates in elections, provided that no bargaining unit representative announcing such endorsement may do so while wearing a fire uniform. No person shall be appointed to or retained in the Department as a reward for political service rendered, nor in any manner be discriminated against because of his or her failure to render such service.