Wal-Mart introduced its own money-transfer service Thursday, moving one step closer to becoming one of the biggest financial services providers in the nation.

The service, called Wal-Mart-2-Wal-Mart, allows customers to transfer funds between any of its 4,000 U.S. locations, enabling the big-box retailer to claim a cut of the market now served by Western Union and MoneyGram.

The recipient can access the money with a pin number. Wal-Mart will charge $4.50 for any transaction under $50, and $9.50 for larger transfers up to $900. That’s substantially cheaper than MoneyGram, which has branches inside Wal-Mart stores across the country.

“We are leveraging our size and our scale to make a difference for our customers,” Daniel Eckert, vice president of financial services for Wal-Mart U.S., said during a call with reporters.

Officials at Wal-Mart say the new service will have broad appeal among the “un-banked” and “underbanked,” the 28 percent of Americans with limited or no access to the traditional banking system. That population tends to use alternative financial firms like check cashers that also offer bill pay and money order services. Over the years, Wal-Mart has tried to siphon off those customers by providing the same products at lower rates.

“Wal-Mart-2-Wal-Mart is really an extension of our broad assortment of everyday financial services that we offer to our customers,” Eckert said. “This is about providing those everyday financial services for less and making sure that they can save a little here and there.”

The company broadened its reach two years ago with the introduction of Bluebird, a prepaid American Express card that functions like a bank account. Wal-Mart aimed the card squarely at customers of the banking industry, which has fought vigorously to keep the retailer from obtaining a bank charter.