The retailer said the claims are "not a reflection of who we are or what we stand for."
According to the New York Times, Wal-Mart failed to notify law enforcement officials after discovering evidence of millions of dollars in bribes by its Mexican subsidiary.
The payments were allegedly to obtain building permits.
The newspaper also reported that Wal-Mart only informed the U.S. Justice Department after learning of the New York Times investigation.
Wal-Mart is Mexico's largest private employer. The company says its latest, ongoing investigation is being handled by outside lawyers and accountants and that it has tightened procedures and expanded training in Mexico.
The Associated Press contributed to this report.