If you shop at grocery stores and pharmacies, you probably hold their discount cards. But do you realize how much information they reveal about you?

Carnegie Mellon economics professor Robert Strauss told WTAE Call 4 Action reporter Susan Koeppen that stores like Giant Eagle and CVS that offer these cards know more about their shoppers than some segments of the government.

"If you're going in with your discount card, not only do they identify you -- they know what you bought, item by item," Strauss says. "They know more about you than what you are willing to tell the IRS."

Koeppen says a group called Consumers Against Supermarket Privacy Invasion and Numbering is so outraged by discount cards that it has dedicated a Web site to the issue (www.nocards.org).

But CVS says it doesn't share specific information about shoppers with manufacturers or direct marketers, and Giant Eagle says it doesn't sell any personal information that identifies shoppers.