Most of the analysis on American Express (AXP) Friday was focused on the relief rally in the shares after reporting a better than expected quarter. Many point out that the quarter was a low quality beat and that American Express is under reserved given its exposure to deteriorating consumer credit.

However I didn’t see any analysis on something a little more interesting. Like most I have an Amex Blue card and recently I failed to pay my bill on time. I got a little busy so don’t spread the word or the credit card police will be knocking on my door. I noticed on my bill that the interest payment seemed a little higher than normal so I did the calculation. YIKES! To my horror I found that the rate had jumped to 27.99%. I thought I borrowed money from American Express not Tony Soprano.

I called customer service whose reps were very polite but told me that you jump to the “default” rate when late on a payment. She said “It’s all in the fine print in that mailer we sent to you.” Has anyone ever read one of those notices? Try it sometime. It’s like trying to read a Citigroup (C) annual report.

The point is that loan sharks make significantly better margins than financial service firms and American Express has recognized the advantages of that business model. Fortunately I have the means and immediately paid off the balance but there must be millions of cardholders who need to carry a balance and for whatever reason missed a payment and are now stuck with the new juice.

In case you haven’t figured it out this is a windfall for credit card companies as I doubt that American Express is alone in this practice. Many may not notice the change for months and I doubt customer service will bring it to their attention. Sure after a period of time they'll review your rate but in the meantime they'll milk this for all they can get.

While credit card companies' fortunes are certainly tied to a weakening consumer, for the next quarter or two they may surprise the bears with better than expected earnings. How long they can play this game is anyone’s guess. If a customer gets in over their head they still have recourse and in the end as we know can always file for bankruptcy. Not much the card companies can do about that. Tony is a little less forgiving and his collectors are a little more persuasive.