Whole Foods is now one of the top organizing targets by the UFCW, yes grouped explicitly with Wal-Mart as one of the worst companies in the industry.
Folks bash the union leadership on this list a lot, but then they often don't even engage in the basic solidarity of supporting organizing campaigns. General boycotts may not be particularly useful, but avoiding companies actively being organized and engaging in union-busting tactics seems the most minimal solidarity called for by leftists.
See http://www.wholeworkersunite.org/ for more on the whole Whole Foods fight.
Nathan Newman