Maintained by the RAF Caucus. This is the page to read first if the words "union" and "caucus" are getting tangled up. It explains what each thing is, how they relate, and where different decisions actually get made.
Put simply: the union is the whole body of members. A caucus is an organized current within it. You are a member of the union first; being part of a caucus is a further choice.
A union is an organization of workers who join together to build power at work — over pay, conditions, safety, and how they are treated. AWU-CWA is a "minority" or "wall-to-wall" union: it organizes Alphabet workers regardless of role or classification, and it does so even where it does not yet hold a formal collective bargaining contract. Membership means paying dues, having a vote, and being part of collective action.
A caucus is an organized group within a larger democratic organization. Its members agree on a direction and work together — running candidates, proposing policy, and organizing campaigns — to move the wider organization that way. Caucuses are a normal and healthy part of a democratic union: they are how members debate priorities and hold leadership accountable.
The RAF Caucus organizes around rank-and-file power: the idea that a union's strength comes from its members organizing their own workplaces, rather than from staff or officers acting on their behalf.
This is the part that most often causes confusion.
So when RAF "endorses a slate," that is a caucus decision to recommend candidates. Whether those candidates win is a union decision, made by all members voting.