The officers and members of the police and paid fire departments of cities of the metropolitan and primary classes and of cities of the first class having a population of more than ten thousand inhabitants as determined by the most recent federal decennial census or the most recent revised certified count by the United States Bureau of the Census shall each receive a salary of not less than three hundred fifty dollars per month. The city council may, by ordinance, at any time, change, fix or revise the salaries of the officers or members of the police and fire departments of such cities, but in no instance shall the minimum salary of any officer or member be less than three hundred fifty dollars per month.