All municipalities in the State of Alabama, whether now or hereafter operating under a municipal government consisting of a mayor and aldermen or of a commission, are hereby authorized at their discretion to employ a city manager with the authority, duties, and liabilities described in this article, whose term of office and compensation shall be as prescribed in this article.

The authority given under this article to employ a city manager and to invoke the provisions hereof shall be exercised by the passage of an ordinance or resolution by the governing body of the municipality so desiring to employ a city manager, which ordinance or resolution shall set a date not less than 30 nor more than 60 days following the date of its passage upon which the city manager shall assume his office.