NEW YORK (CNNMoney) -- Starbucks Coffee Co. has signed on with Square Inc. to process its credit and debit card purchases, the coffee shop franchiser said Wednesday.

As part of the deal, Starbucks (SBUX, Fortune 500) pledged to invest $25 million in Square, a mobile payment platform for retail. In addition, Starbucks CEO Howard Schultz will join Square's board of directors.

By the fall, customers will be able to use the Pay with Square mobile application to purchase their cappuccinos and lattes, said Starbucks, which competes against Green Mountain Coffee Roasters (GMCR) and Dunkin' Brands (DNKN).

Square provides credit card reader applications for smartphones, including the iPhone, iPad and Android, to process transactions.

In an open letter, Square Chief Executive Office Jack Dorsey said the Starbucks deal was a boon for growing his business.