Misrepresentation

No, this is not an illegal practice. If you read the small print on the back of your invitation, it says Pre-Approved simply means that they got your name from one of the credit bureaus as being someone with good enough credit to be eligible for this offer. However, credit is an always-changing thing, so if something has changed negatively on your credit reports since they originally obtained information on you, you could be turned down.

Hope that explains things a little.