It’s the question that often comes when you hand over your credit card at the store: what’s my zip code?

Next time you’re asked, you may want to think twice before handing over the information.

You have to do it when you pay at the pump, but inside a store you have no obligation to give up your zip code.

In fact, saying yes to the question has a big downside.

“What most people don’t realize is there is technology now that with your name on the credit card and the zip code, they can actually find your address,” said Perry.

Retailers can use that information to send you junk mail, which doesn’t sit well with many shoppers.

“I don’t think any of us like that feeling that we’re being stalked by somebody who wants to sell us something,” said one shopper.

In 2011, the California Supreme Court ruled that retailers don’t have the right to require a zip code or other personal information for a credit card purchase.

But stores are still asking.

The I-Team has learned that a federal judge this month approved certification for a class action lawsuit filed against Wal-Mart for the practice.

If the suit is successful, tens of thousands of customers could be entitled to damages in the form of cash or a coupon.

Attorney Perry hopes the ruling will encourage retailers to be more transparent.

“It’s certainly one thing if someone asks you ‘Would you like to be on my mailing list’ and you say yes. Then you’ve given your permission. But to be put on a mailing list that you don’t know about or don’t expect is a completely different issue,” Perry said.

The only time you can be asked to give your zip code during a credit card purchase is at the gas pump – and that’s because you’re dealing with a machine – and it’s meant to prevent fraud.

By the way – you also may want to say no when you’re asked to give your email for an electronic receipt – since the information can also be harvested for marketing information.

For more information on what retailers are allowed to ask, find out here.

Published at 6:12 PM PST on Jan 8, 2016