Even so, such incidents are a test of how far Visa and Mastercard are willing to go to enforce the penalties associated with non-compliance -- particularly when dealing with large merchants, said an analyst at a financial services firm who requested anonymity.

"This opens up some questions on how objectively they will deal with this issue," the analyst said. "Will they pay favorable attention to large retailers like Wal-Mart but be willing in a split second to cut off the mom-and-pop liquor store" that suffers a similar security breach?