What Are Retailers Really Doing With Your ZIP Code?

When it comes to paying with plastic at the cash register, you know the drill. A quick swipe, a signature and the contents of your shopping cart are yours. But sometimes the cashier asks for one more thing: "May I have your ZIP code, please?" So what's a credit card customer to do when a merchant asks for a ZIP code at the cash register? Two states have now declared the practice violates their privacy laws.