James Martin/CNET

Apple Pay has a new credit card in its fold, namely the American Express corporate card.

Unveiled last October, Apple Pay enables owners of the iPhone 6, iPhone 6 Plus and Apple Watch to pay for items on the go via a wireless technology known as near-field communication, or NFC. Other Touch ID-enabled devices, such as the iPad Air 2 and Mini 3 , can use Apple Pay for in-app transactions.

In the US, Apple Pay already supports Visa, Mastercard, Discover and American Express for consumers and small businesses. With the new move, American Express becomes the first corporate credit card to work with Apple Pay, potentially opening up a whole new and wider audience.

Apple has been striving to expand Apple Pay support among credit card companies, bank and retailers, both in the US and the UK. The company has been successful at winning over credit card providers and financial institutions -- more than 400 banks and credit unions are onboard. Signing up retailers is a more complex matter. Apple Pay is currently accepted at 71 US retail chains with 27 more coming. But those are just a fraction of all the retailers in the country. And not every individual store at a supported retailer can handle Apple Pay. In order to accept an Apple Pay payment, a store's point-of-sale system must be equipped with the necessary NFC technology.

Apple Pay also faces competition from similar services offered by other companies. Samsung Pay is being tested in the company's home base of Korea but is set to officially roll out this month for the Samsung Galaxy S6 and Galaxy S6 Edge as well as new Samsung devices. Google has unveiled a mobile payments service called Android Pay. And a group of retailers known as the Merchant Customer Exchange aims to challenge Apple Pay with its own service known as CurrentC.

Apple Pay allows American Express card members to add their eligible corporate card and pay with their mobile devices at contactless merchants in stores, or within participating apps that accept American Express. American Express card holders who use Apple Pay with an iPhone 6 will also receive real-time notifications and details on purchases and a connection to the Amex mobile app to monitor their accounts and gain access to rewards and special offers.