Birkenstock will stop selling directly to and ban third-party sales on the site effective Jan. 1 due to a proliferation of counterfeit products being sold there, according to a memo obtained by CNBC.

Birkenstock USA CEO David Kahan disclosed the decision in a letter sent July 5 to thousands of the company’s retail partners, according to a July 20 report by CNBC.

In the letter, which CNBC obtained, Kahan explained the German footwear brand decided to yank its products from Amazon after concluding it had created “an environment where we experience unacceptable business practices” and that “Policing this activity internally and in partnership with has proven impossible.”