Tech-bro shoemaker Allbirds is calling out Amazon.com for copying a pair of its $95 sneakers made from fine merino wool and selling them for one-third the price, the latest brand backlash against the world’s biggest online retailer.

Allbirds co-founder Joseph Zwillinger says Amazon should mimic its eco-friendly materials as well if it’s going to mimic the look of its trendy sneaker.

“We are flattered at the similarities that your private label shoe shares with ours, but hoped the commonalities would include these environmentally-friendly materials as well,” Zwillinger wrote in a Medium post Monday, offering help in securing the materials. An Amazon spokeswoman declined to comment.

Allbirds is the latest brand to take a swipe at Amazon, which has launched more than 1,000 private-label products — from furniture and tortilla chips to phone chargers and adult diapers. Williams-Sonoma last year sued Amazon, alleging that one of its private-label orb chairs was “strikingly similar” to one sold by its own West Elm brand.

Amazon maintains private-label products represent a small percentage of its overall sales and are necessary to make sure customers can find the products they’re looking for. Some brands are skittish about selling products on Amazon since fakes flourish on the site and they worry Amazon controls too much of the customer relationship. Nike Inc. is the latest brand to stop selling directly to Amazon, preferring to pursue a direct to consumer strategy.

Democratic presidential candidate Elizabeth Warren has proposed prohibiting Amazon from competing against the third-party merchants that generate most of the company’s sales.