Birkenstock CEO Dave Kahan told his resellers in an email that Amazon.com's (AMZN) - Get Report new inventory buying program aimed at selling products not currently approved for the online retail site is "pathetic" and an "assault on decency," CNBC reported.

Amazon has recently started buying products at full price from third-party merchants and selling the products to customers on Amazon.com. Most of the third parties sell brands that have declined to do business with Amazon, just as Birkenstock chose to do in last year on increased concern about counterfeit shoes.

Amazon has offered to buy Birkenstock shoes through third parties to keep the brand on its site even if the company has pulled out of doing business with Amazon. Kahan issued a serious warning to his sellers: "Any Authorized retailer who may do this for even a single pair will be closed FOREVER. I repeat, FOREVER."

The new strategy gives Amazon control over a brand's global distribution. "It's only a matter of time before brands start challenging this in court," Buy Box Experts partner James Thompson said. "Brands aggressively protect their trademark both domestically and overseas."

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