My favorite was MBNA. They gave us a large credit line; as the interest rate was cheaper than the bank's, I financed my job re-location with this card. Next thing I knew, my interest rate went from 6.8 to 19.9%. I never had late payment, my payments were always for more than the amount, and were always recieved at LEAST a week before they were due.
Why, you ask? I called and asked why. The loan dept. said that my interest rate was dependant upon how much I used of my available balance. You see, the more you use; the greater the risk to MBNA. So, I paid the amount in full, closed the account, and have requested to be placed on a Do Not Contact List.
I think this behavior should be illegal. I was fortunate in that I was able to pay off the full amount; others will not be so fortunate. If I had been late, if I had over-charged; that would be a different matter entirely. But to simply kick the interest rate up because a person uses the credit limit that the company offered seems preposterous.
Try this from MBNA. When I was in grad school I had a 42K credit limit. I didn't ask for it and having gone right from college to grad school I never had a real income. If I had run it up and defaulted they would have nobody to blame but themselves. No other type of lender in the world would give a college student and unsecured loan in that amount.