According to a Sunday Wall Street Journal report, Amazon has been fighting the practice—which is particularly pronounced in China, though also present in the U.S.—since May, when management was tipped off that it was happening.

Brokers are apparently arranging payments from merchants to Amazon staff for data on sales, advertisement bids, and the number of times people search for and click on certain products. They are also facilitating bribes to staff for deleting negative reviews, or handing over the contact details for those who left negative reviews so merchants can try to convince them to amend the low-star ratings they left.

According to the Journal piece, brokers in China identify Amazon staffers who have accounts on the WeChat messaging platform, and approach them with offers for payment. After Eric Broussard, Amazon’s vice-president of international marketplaces, was alerted to the practice in May, the company moved around key executives in the country in an attempt to “root out the bribery,” the paper reported.

Reviews are a major factor that Amazon (AMZN) takes into account when deciding how prominently to place products in its search results—and search rankings are make-or-break in the e-commerce world.

“We hold our employees to a high ethical standard and anyone in violation of our Code faces discipline, including termination and potential legal and criminal penalties,” a spokeswoman told the Journal.

Amazon is known to regularly sue merchants that arrange fake reviews on its platform. The problem is so rampant—across many platforms; not just Amazon’s—that consumer tools are available in order to flag up potentially unreliable reviews.

A man was jailed in Italy earlier this year for offering hospitality businesses fake reviews on TripAdvisor.