Two leading US retailers – Wal-Mart and Best Buy – will not allow iPhone 6 and iPhone 6 Plus users to make NFC-based payments in their stores when Apple Pay launches in October, according to The Wall Street Journal.

Both retail giants are backing MCX, a rival payment service that is supported by many leading US chains. Earlier this month MCX soft-launched its own brand and app called CurrentC.

Apple has proved adept at gaining support for its new payment service among leading credit card firms, major banks and some retailers.

MCX’s backers include a rollcall of leading chains such as Dunkin’ Donuts, GAP, Kmart, Old Navy, 7-Eleven, Sears and Target, as well as Wal-Mart and Best Buy.

However, a national rollout of CurrentC is not scheduled until next year. Also, it is not clear whether all its backers will actually introduce its service.

Apple announced last week a number of leading retailers that supported its payment service including Bloomingdale’s, Disney Store, Macy’s, McDonald’s, Staples, Subway, Walgreens and Whole Foods Market.

There is no crossover between Apple’s supporters and MCX’s membership.

However, Whole Foods Market does already have a relationship with Square which handles payments at some of its stores including sandwich counters, juice and coffee bars, pizzerias, and beer and wine bars.

Apple has proved strong in signing up the financial community. The three major payment networks, American Express, MasterCard and Visa, are all on board with Apple Pay, as well as card issuers including Bank of America, Capital One Bank, Chase, Citi, and Wells Fargo.