Thing is you have to be very careful what you argue about as you will get no backing from the union when push comes to shove and management will just find away to force you out if you become aapain in their arse.
, I made a complaint about a health and safety issue, union agreed with me and said they would take it further even my manager agreed with me , after it went to next level management the reps and manager both denied they said they agreed with me and there was absolutely no problem .
I then got warned by a co worker that he had overheard the manager telling the reps that he wanted me sorted by the end of the week. Next day I got called into a meeting and told me my job was no longer required so they were demoting me , changing my shifts and cutting my wages.
I called the outside union rep and he promised me he would come to the further meetings and that I had nothing to worry about . He never turned up to one. I ended up going off sick with anxiety and depression but managed to get another job . So never went back.
Sorry for the long off topic post but after paying in and being very pro union for over 30 years I wouldn't ever sign up for one again.