In my job it's a mix of TUs, RMT, TSSA, Aslef and on the buses, Unite have some members.
I'm in the RMT, who will strike if there's no other option. Evening Standard calls us hardliners. Ha! The RMT rep most station staff, cleaning staff and the people you don't see like Track maintenance. We've not been militant since Bob Crow passed away. Mick Lynch knows how to deal with the media, he's very good at it, but he's no communist.
TSSA used to rep the ticket offices, but now they rep generally those people who don't like striking. They hold out a lot longer before agreeing a deal or taking IA.
Aslef are the main union for train operators though some belong to the RMT.
Unite take anyone.
I pay £23 a month in subs. For that I get a free diary, freel legal advice, access to a credit union, and assistance from a rep in employment matters. I've had my money's worth, believe me.
I don't go to meetings but they are where members raise issues. There is a hierarchy before it reaches the assistant General Secretaries. Matters can be acted on locally, regionally or nationally. If no agreements are settled then members are asked to vote for IA. And that's when the General Public find out the poo has hit the pan, and likely to cause them inconvenience. Before Royal Mail employees, members of the CWU went on their first strike, they had been negotiating with the CEO for a year. In my job, on the tube, we have similarly been trying to get a deal for 18 months. We don't just "walk out" like some media will lead you to believe.
I also vote for the union executive and I vote for who sits on the Pension Fund.
If there is a strike called I get an email, and a text. I also keep up to date on Twitter. Not everyone takes part, either because they aren't in the union or because they are, but don't agree with why the IA is needed.
Secondary Action: This is illegal. Also, you are only allowed six members on a picket line. We can talk to people about not crossing the picket line, but we can't prevent them from doing so.
If you can join a union do. The more people in your workplace with union membership means greater bargaining power when talking about pay, terms and conditions.