I'm an old-timer but have NC just in case.
For reasons discussed at length on this board I am not a member of UCU.
The branch secretary is in my department and on a recruitment drive. He's emailed me personally before about joining UCU but I've ignored these emails. He's bent my ear in-person a couple of times too. I was non-committal in these conversation because it was out-of-the-blue and I wasn't ready/willing for a long/deep conversation about it.
In the new academic year, me and this colleague are working together on a project (administration, thankfully he's not in my research or teaching area). The issue of me joining UCU will come up pretty quickly and pretty regularly I'd imagine. I'm not a confrontational person so I'm after some ammunition to stave him off which won't also get me into bother for being a TERF.
I should say that this colleague is a woke-bro pronoun person with a little fan club of smug he/her/theys that I'm keen not to provoke.