NEW YORK ( TheStreet) -- Bank executives' heads are on a swivel as they face technologies that threaten to eat into market share. PayPal has made inroads into the consumer payments market. Google ( GOOG) and Apple ( AAPL) have popped mobile wallets into their smartphones. And Wal-Mart ( WMT) has taken incremental steps into the banking business with a prepaid banking card called Bluebird available in more than 4,000 of its U.S. stores. Now American Express ( AXP) has targeted banks from a perhaps-unexpected front: social media. Last week, Amex announced a program that enables Twitter users to tweet #hashtags to buy products and gift cards. In this outgrowth of Amex's Sync program -- which has delivered special offers and mobile coupons to customers via Twitter since March -- all Amex customers have to do is sync their credit card with Sync and tweet special #hashtags to start buying products and gift cards from eligible companies. Brand names such as Sony ( SNE), Amazon ( AMZN), Microsoft's Xbox 360 and Urban Zen have signed up to participate. "Based on the initial success of Amex Sync for offers, we know there is significant power in combining our assets with Twitter's platform," says Leslie Berland, a senior vice president at American Express. "Now 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." Any products bought via Twitter will be shipped free to customers within two days, American Express says. You can check out the full menu of options here. There's no way of knowing the demand for buying gift cards and products through Twitter. But with more than 500 million existing "tweeters" and 150,000 users signing up every day, banks can hardly ignore the tsunami heading their way. Even it if it is a tsunami of 140 words or less.