Because when you have dozens or hundreds of union members, you need stuff to be organized, as in every organisation?<p>Unions are very differently organized depending on the country, their political leaning (or lack of thereof), their industry... 
For instance, it looks like that in the US, the Organizing Model[1] is prevalent, which means that a large workforce has to be employed by the union<p>From the media, it seems to me that unions in the US are generally less politically organized than in Europe. For instance in France, unions are almost always politicaly leaning in one way or another, from CNT (&quot;anarchist&quot; union), CGT (historically linked to the french Communist Party) and CFTC or FO (historically split from CGT by anti-communist organisations) and going sometimes to the right end of the political spectrum such as Alliance&#x2F;CFE-CGC (french readers please forgive my broad simplification, I do know that it&#x27;s much more complicated than my summary...). My limited knowledge of trade unions in Belgium and Spain comes to a similar analysis<p>However, from how they are portrayed in the media, it seems to me that unions in the US are rather &#x27;trade 
based&#x27;, for instance &quot;the&quot; teachers union, or the truckers unions, etc. In contrast in France a teacher could be affiliated to CGT Education or FO Education (depending on their personnal preferences&#x2F;political leaning), which are in turn members of a larger &quot;confederation&quot; such as the CGT. In my (very simplified) example, the &quot;teachers CGT&quot; and the &quot;truckers CGT&quot; can and do band together and strike&#x2F;picket together when an issue impact both teachers and truckers.
In my simplified example, CGT Truckers also strike in support to teachers during large movements.<p>Is this also a thing in the US? It seems to me that it&#x27;s not the case?<p>[1]<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Organizing_model" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Organizing_model</a>