There are several flavors of labor unions. Some represent entire industries, but in this case they are joining a federation of smaller unions that are company specific. So the titular IAM is more like a parent company, or franchise, and to an extent it can get somewhat arbitrary, but generally if there’s a union that already represents a similar industry as one’s own, that’s usually the one to choose, as they will have an established base of members, relevant expertise for preparing for a vote and negotiating contracts. Even for somewhat novel professions, there’s generally going to be a similar analog to start with. The nominal profession(s) (in this case, machinists) were simply the O.G. industry that kicked it all off back in the day. The IAM is part of the AFL-CIO, and represents more than 200 industries in North America according to Wikipedia. A labor union does what it says on the label, and represents a unified coalition of workers. Most of these kinds of unions have been around for far longer than even some of the industries they represent. The United Electrical, Radio & Machine Workers of America also represents teachers, clerical workers, hospital workers, and railroad operators. Their power is derived from their numbers, and their reach is increased with a diversified pool of industries. They are incentivized to develop branches and provide a big tent in order to grow their influence and power. As long as the members’ interests are aligned, the specific jobs they occupy aren’t strictly relevant, however there needs to be some level of commonality in order to provide them with a meaningful amount of leverage during contract negotiations. If the organization is too untethered between industries, then things like labor strikes won’t carry the intended message very effectively.

—-

Note: I am not a union official, or even a member, and this is entirely based on my own (possibly flawed) understanding as a history and poli-sci enthusiast. Take it with the requisite grain of salt.