TOKYO - Japan's largest convenience store operator Seven-Eleven Japan Co. has issued a warning to its franchisees nationwide that unauthorized resale of merchandise featuring popular anime and game characters may be rampant, multiple sources close to the matter said Thursday.

Some owners and employees have been caught setting aside merchandise before its release or buying up large quantities to sell on resale sites. Such activity is seen as a betrayal of consumer trust and likely to call into question the governance structure of store operations.