Reading the RMT▸ site, one question, why do they keep referring to the guy as "Brother"?
Surely 'Comrade' is non-gender already?
Either term is redolent of the kind of socialism that looks like a damp breeze block and smells of stale wee. Why do they feel the need to use any kind of title?
Why do they use Brother like that?
Historically, brother would have been common in several kinds of groups that the unions either grew out of or felt some commonality with - guilds, secret societies and fraternities, and nonconformists during the revival of the early 1800s. While unions may not have been religious, those primitive methodists, brethren, etc. were clearly anti-establishment, and their habit of squabbling about rules and procedures and forming splinter groups pre-echoes left-wing politics (I'm thinking of the 70s). So brother was an obvious choice as an egalitarian greeting and title, even if some of those precursors had hierarchical titles like master too.
In Britain, the prior use in religious orders wasn't a problem, given the lack of monks. In France it was, as the left was universally anti-clerical and the church was powerful, so camarade was adopted from military and revolutionary usage. That was reinforced when the Russian communists took over the various internationals, and camarade became the standard translation of tovarishch. In Germany, Kamerad was not acceptable as it was used in right-wing militaristic societies, and presumably Bruder wasn't accepted over much of Germany either, so I think Genosse got adopted instead. Kamerad of course was and is much better known to non-Germans, no doubt largely due to WWI (and II).
But why do they still use it (and comrade)? On one level we don't use titles, or this kind of greeting, much today, so they probably could drop it if they really wanted to not look like they are living in a parallel but slower-moving universe. But similar terms are used by some sub-groups, or self-conscious minorities. Unions might justifiably feel they have been persecuted, and have become more of a minority, but surely not to the extent of preparing to go underground*.
Incidentally, is Bro' in the RMT's text just a written abbreviation, or do they say "bro" and risk being attacked for cultural appropriate or suchlike?
*Though the RMT of course already are Underground.