American Express Co. cardholders who make known their presence at a merchant location using foursquare, a location-based mobile check-in service, will be eligible for special offers in a new program from the two companies. Sports Authority, H&M and Union Square Hospitality Group are the first participating merchants. AmEx expects to add more merchants in coming months.

AmEx cardholders who have foursquare accounts must register on a special AmEx web site to participate. AmEx says this program eliminates the need for coupons or special codes to redeem offers. Upon checking in at a participating merchant, the system connects the offer to the card. The cardholder simply pays with that card to redeem the offer, AmEx says.

For example, an AmEx cardholder who checks in at a Sports Authority store is eligible for a $20 discount on a purchase of $50. At H&M, the consumer gets $10 when she spends at least $75. The offers show up as credits on their card statements.

The AmEx tie-in is a big change for foursquare, the local deals company says. “Partnering with American Express to offer specials to their millions of cardmembers on a nationwide basis not only allows us to provide a completely seamless redemption experience to both users and merchants, it also enables merchants to really measure the success of their offline marketing efforts with foursquare,” says Dennis Crowley, foursquare CEO.

AmEx sees a good fit between its cardmembers and foursquare. “We appreciate that foursquare appeals to a younger customer who is excited by the check-in experience offered by location-based social technology,” says David M. Wolf, AmEx vice president of interactive development. “This is a natural fit to the couponless offers enabled by the American Express Smart Offer APIs technology.”

AmEx’s Smart Offer API enables the linking of the AmEx card to the foursquare account and electronically connects the merchant offer to the cardholder account. When enrolled cardmembers use an AmEx card to pay, they receive a message indicating that a statement credit will be issued. This eliminates the need for merchants to train their front-line staff to redeem the offers, AmEx says.

Foursquare and AmEx tested this system at South by Southwest Interactive, a technology event held in March.