CardSystems Solutions Inc. "has not corrected, and cannot at this point correct, the failure to provide proper data security for Visa accounts," said Rosetta Jones, a vice president at Foster City, Calif.-based Visa, in a statement.
She said banks that issue Visa cards would have until Oct. 31 to replace CardSystems with one of the hundreds of other payment-processing companies in the U.S.
American Express also notified CardSystems it would sever their relationship as of October, spokeswoman Judy Tenzer said. CardSystems was a small part of American Express' network, handling less than 0.5 percent of its transactions, she said.
Representatives for Atlanta-based CardSystems did not return calls seeking comment.
CardSystems told the FBI it learned of a potential breach of its computer network on May 22, and the break-in was publicly disclosed last month. The agency has not disclosed any details of the investigation.
While information relating to 40 million accounts was laid bare in the break-in, credit card companies have said at least 200,000 were known to have been stolen, primarily MasterCard and Visa cards.