Little to say other than they are a craft union, with training programs for members. The late AFL Presidident George Meany came out of the plumbers. They were generally known around my parts as a father-son union. That is son followed father into the trade. Pretty conservative.
A number of years ago the local UA let us use their hall when we (our UE local) had a lockout/strike on. They were ok, decent enough about things.
Here's some UA membership websites linked from the Association of Union Democracy (AUD)
http://www.uniondemocracy.org/AUDLinks/RNFLinks.htm#UA
Good luck.


Im speaking of the The United Association of Journeymen and Apprentices of the Plumbing and Pipe Fitting Industry of the United States and Canada.
Im starting to look into plumbing unions (In traiing right now), they represent the most plumbers here in Quebec, but there are some pretty cool local unions to choose from too. One which actually has some fairly lefty positions on things, the CSN, has a construction section, and their Montreal Council is a very progressive place to be having political battles (there is even a small but real nefac presence).
Im probably just going to go for density, but a little history or current opinions would be helpful.