Search giant added US card firm into cloud version of payments platform without authorisation.
The new cloud-based version of Google Wallet claims to accept credit and debit cards from Visa, MasterCard, and American Express, enabling in-store and online payments.
However, AmEx spokesman Brad Minor has said: "they [Google] haven’t gotten our approval for the additional use," according to AllThingsD.
While Google may be using the AmEx name without formal certification, the credit card firm has been used in other payment tools from the search firm, but Minor assures it could block the use in the cloud update at any time.
This prompted a Google spokesperson to say: “For many years, we’ve accepted American Express, Visa, MasterCard and Discover for online and mobile transactions.
"The latest version of Google Wallet extends these same benefits to people who choose to use the Google Wallet app to make purchases in-store. We are in active discussions with American Express and look forward to working together as partners as the world embraces digital payments."