Amazon’s Japanese headquarters in Tokyo have been raided by the country’s fair trade watchdog on suspicion of violation of antitrust regulations.

The Japanese Fair Trade Commission (JFTC) said on Thursday that Amazon Japan was being investigated after allegations that the company improperly asked suppliers to shoulder part of the costs of discounting their products on the retail site. Amazon Japan said Thursday that it was “fully cooperating” with JFTC, but declined to comment on the details of the allegations.

Local media the Asahi Shimbun daily reported that the firm may have demanded suppliers pay a “collaboration fee”, measured as a percentage of the selling price of the product. The Kyodo news agency, citing unnamed sources, said the fees were to cover discounting.

Public broadcaster NHK reported that Amazon told suppliers it would stop working with them if they did not pay the fees.

The JFTC declined to comment.

Amazon Japan has faced regulatory scrutiny before. In a recent antitrust probe, which involved raids on Amazon’s Tokyo offices in 2016, the JFTC found the firm had required suppliers sell items on Amazon Japan at the same or lower price as any listings they may have on on other platforms.

Japan’s antitrust law prohibits a firm from abusing a superior bargaining position to illicitly make a business partner accept unprofitable trade conditions.

The JFTC ended its probe in June after Amazon Japan agreed to drop the practice.

Amazon has been operating in Japan since 1998, with its Amazon.co.jp store front opening in 2000, making it one of the first of the US retail firm’s international expansions. Amazon Japan follows the model established by the firm’s US site, including its Marketplace where third parties can list and sell goods through Amazon’s storefront.

The firm has offices in the Japanese capital and in Osaka, as well as 13 fulfilment centres and five Prime Now warehouses for its same-day delivery services. The company last year reportedly agreed to pay up to 40% more to domestic delivery service firm Yamato, which said its workforce was struggling to keep up with rising demand for package delivery.