I'm pleased to learn that your workplace has a union, Gee.

There are a couple of issues I would like to pick up on here.

Union set up:Trade union legislation here in the United Kingdom was amended some years ago, under the Thatcher administration, to remove the "closed shop" practices that had existed until then.  Previously, unions in many companies were able to insist on employees being members of the union. Nowadays, that is not the case - employees can achieve union recognition if they fulfil certain criteria, but not all employees in a company that is "organized" have to belong to that union.  They may belong to another union (but the other union may not have recognition - negotiating rights - in that company - or no union at all. A number of people won't join unions for all sorts of reasons: they see no value in it (until they need representation), moral grounds, they object to the particular union chosen, they "can't afford" the union fees, or they object to paying a political levy as part of their subscription fees.  There is an escape clause enshrined in law to the latter objection.  If your union is affiliated to a particular political party and you don't wish to fund that party, then you can sign a special form releasing you from paying the levy.

Who tells what and to whom:It is management's responsibility to announce any pay increases to all staff.  It is the union's responsibility to communicate with its members and, indeed, to achieve the best possible outcomes for its members.  If you are not a member of the union, you will not, unfortunately, receive any information from the union reps - only from your employers.

That said - congratulations on your pay increase.  A lot of companies are not funding increases this year, so you are very fortunate.