Western Union shares were down 7.1 percent in premarket trading, while those of MoneyGram International Inc, which currently provides money transfer services for Wal-Mart, were down 14.6 percent. Euronet was up 4.2 percent.

The service, to be launched on April 24, will let customers transfer money to and from more than 4,000 U.S. Walmart stores at what the company says are much lower fees than those of other such services, Wal-Mart said in a press release.

Money transfers through MoneyGram will remain available for customers wanting to send money to a location other than a Walmart store, Wal-Mart said.

For the retailer, the new service is an effort to bring more shoppers into its stores amid declining traffic and boost finance revenues.

Wal-Mart U.S. last year got about 1 percent of annual sales from financial services such as money orders, prepaid cards, wire transfers, check cashing and bill payments, according to its latest annual report. The company offers those services at its Walmart MoneyCenter locations and customer service desks.

Customers using the Walmart-2-Walmart service will be limited to $900 in transfers per day because higher amounts require the sender provide much more information.

(Reporting by Phil Wahba in New York; Editing by Paul Simao)

By Phil Wahba