Nothing in this article shall be construed to prevent employees of the Commonwealth, of its political subdivisions, or of any governmental agency of any of them from forming associations for the purpose of promoting their interests before the employing agency and, if they are employees of a county, city, or town or local school board that has, by a local ordinance or resolution as provided in § 40.1-57.2, authorized its employees to engage in collective bargaining, from doing so as provided in such ordinance or resolution.