American Express announced that members who synchronize their cards with Twitter can take advantage of offers "tweeted" by the financial services company.
American Express will promote products in messages fired off at Twitter. Card holders buy items by tweeting indicated hashtags, with their accounts being charged accordingly.
Depending on the offers, products will be shipped to buyers or picked up in shops.
"We're leveraging our unique technology and closed-loop network to introduce a seamless solution that redefines what's possible in the world of social commerce," said American Express senior vice president Leslie Berland.
"We know there is significant power in combining our assets with Twitter's platform."
American Express said cardholders will be able to buy Sony, Amazon.com, Xbox 360 or Urban Zen products in tweets by using special hashtags, or words preceded by the "#" symbol.
Twitter and American Express have worked together in the past with alliances that let cardholders take advantage of discounts offered in coupons tweeted by merchants.