Apple’s new mobile payments service has been blocked by US stores including CVS and Rite Aid that have signed up to a rival wallet app, setting the stage for a showdown between the technology giant and some of the largest US retailers.

The two pharmacy chains are part of a consortium called the Merchant Customer Exchange (MCX), which includes Walmart and Best Buy, the electronics retailer, that plans to introduce an alternative mobile payments system called CurrentC in the coming months.

“Given that we are still in the process of evaluating our mobile payment options, Rite Aid does not currently accept Apple Pay,” the company said. “We are continually evaluating various forms of mobile payment technologies, and are committed to offering convenient, reliable and secure payment methods that meet the needs of our customers.”