I just heard a teaser on TV about how shopping at the "wrong" store can lower your credit limit. That definitely peaked my interest, so I googled around and found this segment of Good Morning America on exactly the issue: A guy with a stellar credit history gets his Amex credit limit slashed by $7K because he shopped at a certain store. Apparently, customers that shop at such store tend to not pay their credit card bills, so Amex is assuming he will behave like them. Amex won't say what the store is - but the only "new" store at which the guy shopped was Walmart, so we can reach our own conclusions as to where Amex doesn't want you shopping.
Now, I hate Walmart as much as the next person (just watch the Walmart Movie and you'll know why), but give me a break!
Amex is not the only company that has done this - another one was fined by the FTC for reducing the credit limits of customers who went to marriage counselors and auto shops (I kid you not!). I have to admit that I barely pay attention to our credit cards, but I will start to do so now! This behavior is ridiculous.
Here is the Good Morning America segment from last January: