Starbucks is to offer Square’s card reader for sale in its 7,000 outlets in the US, the latest instance of the strategic alliance between the two companies.

The coffee chain is selling the reader for $10 but customers can redeem the fee if they are new to Square.

The payments firm struck a deal with Starbucks in the summer to process its transactions and enable customers to pay in the coffee chain using the Square Wallet app.

And Starbucks became an investor in Square as part of the same deal. However, the current initiative was not mentioned at the time of the alliance.

When fitted onto a smartphone or tablet, the Square card reader enables merchants to process card payments. It is a product aimed at the kind of small businesses who previously did not accept payments by credit or debit.

So far the coffee chain does not use the Square card reader to process payments from customers, despite the fact they will now be selling the reader to them.

Square already has multiple agreements with US retailers as it fights to maintain supremacy in the card reader market which has become increasingly crowded.

Last month, payments vendor Verifone said it would stop offering its dongle directly to small merchants, in a sign of how competitive the market has become.

Square’s card reader is now sold in over 30,000 locations across the US including AT&T, Walgreens, Staples, FedEx Office, Apple, Wal-Mart, Best Buy, Radioshack and Target.