As of January 27, 2013, merchants, online and off, can add a surcharge to every purchase made with a Visa or MasterCard credit card. They can't add the surcharge on debit card purchases. Note that state laws in California, Colorado, Connecticut, Florida, Kansas, Maine, Massachusetts, New York, Oklahoma, and Texas prohibit or restrict credit card surcharges.
The fee allows merchants to recoup the fees that they pay to process the credit cards. The fee can be from 1.5 to 4 percent. The merchant can only charge what they pay, not more.
Merchants must disclose at the store entrance that they are imposing a surcharge. They also have to disclose at the cash register what the surcharge amount it. It must also be listed on your receipt. Online merchants must disclose they are imposing a surcharge on the first page that mentions credit cards.
So, will you see a surcharge? Probably not. Even though merchants can legally charge this fee, many won't.