(Reuters) - Wal-Mart Stores Inc (>> Wal-Mart Stores, Inc.) said on Thursday it was launching a new domestic money transfer service called "Walmart-2-Walmart" in partnership with Euronet Worldwide Inc (>> Euronet Worldwide, Inc.) subsidiary Ria Money Transfer, competing directly with Western Union Co (>> The Western Union Company).

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 it says are lower fees than other such services.

Western Union shares were down 4.6 percent in premarket trading.

(Reporting by Phil Wahba in New York)