Some Chase credit card users report that their cards were unexpectedly canceled.
When trying to use the cards, they were declined and later informed that the card was closed. There seems to be a recent uptick in this activity, so keep a close eye on any Chase credit cards that you have.
So far, it's tough to say if this mostly affects Washington Mutual customers or if anybody with a Chase credit card is at risk. Wamu cardholders have plenty of complaints (see Wamu Cards Absorbed by Chase), but some longtime Chase customers have been fired as well.
I don't think there's a clear explanation why the cards were canceled. This is another sign of a scary environment where you should pay close attention to your credit, where you use your cards, and your monthly payments.