The second power reserved by the people is the simple referendum which may be exercised and ordered as to any ordinance which has passed the City Council and the Mayor, or which has been passed over the Mayor’s veto as provided in this Charter, either upon a petition signed by a number of qualified voters equal to not less than 8% of the total number of votes cast for the office of Mayor at the last preceding municipal general election, or by the City Council itself without petition: Provided; That this section shall not apply to ordinances necessary for the immediate preservation of the public peace, health or safety as provided in this Charter, nor to ordinances relating to the annual budget or the capital expense budget, making or repealing any appropriation, fixing the salaries or wages of officers or employees, authorizing or repealing the levy of taxes, or any repealing ordinances adopted by the Council in compliance with a referendum petition. The fact that the ordinance is already in effect shall not bar the referendum procedure.