California Sen. Barbara Boxer, citing a report by a CBS affiliate in Sacramento, is calling on the Federal Trade Commission to launch an investigation into whether Wal-Mart is ripping off customers across the country by not refunding the full purchase price of items that are returned with a gift receipt.

In an undercover sting, CBS News says it spent a total of $106.85 at Walmart stores in Sacramento and Philadelphia but only received $62.32 in gift receipts.

"It is unfair for retail stories to take advantage of customers returning items with gift receipts," Boxer wrote in her letter. "In most circumstances, people returning gifts are unaware of the cost of the gift, making it easy to take advantage of these customers. A gift receipt should be honored at the identical amount originally paid for the item."

The senator said the agency should investigate the allegations to ensure that the practice is not being repeated as a matter of policy across Wal-Mart or other national chains.

An FTC spokeswoman confirmed to FoxNews.com that the agency had received Boxer's letter and will respond. She said the agency cannot respond beyond that.

Wal-Mart spokesman Lorenzo Lopez told FoxNews.com that the company sent a high-priority notification to store managers across the country to make sure items were being properly refunded.

"From our standpoint, we take these matters seriously and are committed to satisfying our customers," he said. "It's our expectation to refund our original purchase price when receiving a gift receipt."

Lorenzo said when the company officials looked into the matter, they found that there was "some confusion about how to process those returns."

"We believe we've taken the necessary steps to address the matter," he said.