According to the newspaper, which did not give figures, employees of the online giant sell internal data and other confidential information — usually through intermediaries — to merchants who sell their goods on the US giant's website.
On Amazon, customers can buy products sold directly by the company along with goods from many other merchants.
The practice under investigation is a violation of company policy. It is particularly present in China, the paper said, citing the example of intermediaries in Shenzhen working for group employees and selling information on sales volumes for payments ranging from 80 to more than 2,000 dollars.
Reached by AFP, Amazon did not immediately respond.
Fake reviews by purported customers are among the concerns of the internal probe, the report said.
According to The Wall Street Journal, Amazon has been investigating this topic for months. Amazon employs approximately 560,000 people worldwide.