Also....when contract negotiation time rolls around....there are three sets of interests in play....Management...Members....and the Union Organizational interests. Sometimes....nay all the time...management and the union leadership interests do not necessarily coincide with the Members interests, needs, goals, and desires.
Done right...Unions can be a good thing....but most seem to go all pear shaped at some point in time.
The very best defense against a Union is a competent, connected, honest management that values their people and see them as "people" and not "assets", "staff", or "overhead".