Japan's Fair Trade Commission has raided the offices of Amazon.com's local unit on suspicion of pressuring retailers to offer products at lower prices than on rival sites. The Nikkei business daily cited unidentified sources with knowledge of the case but did not say when the raid took place.
Japan Fair Trade Commission did not confirm the report.
Amazon's practices toward retailers and e-commerce partners have also come under scrutiny in Europe.
Germany's Federal Cartel Office began an investigation in November into Apple and Amazon after complaints that publishers were being forced to accept "unreasonable conditions" for the marketing of audiobooks.
And the European Union last year opened an antitrust investigation into Amazon's e-book business, examining whether clauses in contracts prevented publishers from offering more favorable deals to Amazon's competitors.