Both brick-and-mortar and online businesses can now charge up to 4 percent of the transaction cost.
They've always had to pay a fee to the credit card companies. But after a settlement with those companies, they can pass the fee along.
"There has to be a sign conspicuously displayed indicating that they do surcharge, then at the cash register and on your receipt they have to clearly disclose what the surcharge is," said Adam Levin, Credit.com.
This applies only to credit cards, not debit cards.
Some big chains have already said they won't charge the fee.