I have only encountered one person who doesn't want to shop at Wal-Mart because it's full of 'dirty poor immigrants who can't speak English' but IMHO she was pretty ignorant. She said this to a pair of english as second languge immigrants. WTF. I guess she thought we were "okay" because we were educated. She was also always saying things in training (this was for work) that would make everyone including our trainer pause, gasp, or say 'wth'? Mind you, this is someone who for a living would have to interact daily with the 'dirty poor immigrants' she didn't want to shop with.
Other than her, I haven't encountered anyone who won't shop at Wal-Mart because they don't like poor people. Most of the labor activists I know come from poor/working class backgrounds themselves or else have enough awareness around class issues that if they do have a gut reaction against being with 'unwashes masses' they understand it for -isms and privelege and self-monitor and work on it.
The only 'group' of people I can think of who might be classist veiled behind good intentions (because I guess, you know, we've gone there with group stereotyping) are green yuppies. The folks who shop at Whole Foods (who have their own history of labor issues) and Trader Joes and buy premium fair trade coffee and $85 organic cotton yoga pants. Because actually, they really really REALLY don't want to rub elbows with commoners.
Dude, I lived in a whole city with folks like that!