You can find the UCFW affiliate in your area at http://www.ufcw.org/.
The phrase "companies represented by UFCW Local X" strikes me as pretty misleading. They may represent some workers, but certainly not customers, suppliers, management, or shareholders (as Ben Stein calls them, "widows and orphans").
Anyway, I was interested to find out that several places I shop are unionized--CVS, Macy's, and Safeway--and others--Walmart, Whole Foods, Target, Wegman's, among many more--presumably are not.
Whatever your preferences, it's good to know.
P.S. Incidentally, a report from the Bureau of Labor Statistics last week noted that public employees made up a greater share of union membership than private sector workers in 2009--the first year that's ever happened. Federal, state, and local government workers were 37.4% unionized (7.9 million workers), while only 7.2% (7.4 million) private sector workers belonged to unions. Apparently union membership hasn't been this low since 1900.
P.P.S. Also, the new Cato Journal seeks to answer the question, "Are unions good for America?" I haven't had a chance to dig in yet, but it looks like an interesting read.