Sec. 1. In all incorporated cities and towns having a population of two hundred and ninety thousand (290,000) or more, according to the preceding Federal Census, the governing body of such city or town is hereby authorized to formulate and devise a pension plan for the benefit of all employees in the employment of such city or town. Before said pension plan as devised and formulated by the governing body of such city or town shall become effective, said entire pension plan shall be submitted in ordinance form by said governing body to the qualified electors of such city or town and be approved by said qualified electors at an election duly held. Said ordinance containing said pension plan when submitted to the qualified electors for approval, shall be so worded as to authorize the governing body of such city or town to either appropriate yearly out of the general revenue of such city or town a sufficient sum to carry out said pension plan, or to levy yearly a general ad valorem tax sufficient to provide for said pension plan, said sum to be appropriated yearly or to be raised by taxation, to be in addition to whatever sum, if any, to be contributed by the employees of such city or town to the pension fund of said pension plan.