Citing sources related to the matter, Kyodo news agency said the online retailer is suspected of possibly asking suppliers to shoulder part of the cost incurred from selling their products at a discount on Amazon Japan.
Amazon Japan said it was cooperating fully with regulators, declining to elaborate.
Amazon Japan had come under regulatory scrutiny before. In a previous anti-trust probe, the Fair Trade Commission found the firm had required suppliers that sell their products on multiple
platforms to list them on Amazon Japan at the same or lower price.
Amazon Japan agreed to drop the practice and the regulators ended the probe last June.
The Japan Fair Trade Commission declined to comment on the case.