allbirds skitch Allbirds/Amazon

Allbirds cofounder Joey Zwillinger is fed up with Amazon for selling shoes that look almost identical to Allbirds‘ wool sneakers for less than half the price.

Zwillinger penned an open letter to Amazon CEO Jeff Bezos Monday that criticized the online retail giant for not committing to using the same sustainably sourced materials as Allbirds.

„Please steal our approach to sustainability,“ Zwillinger wrote. „If you replaced the oil-based products in your supply chain with this natural substitute (not just for one product, but all of them), we could jointly make a major dent in the fight against climate change.“

An Amazon spokesperson was not immediately available to comment on Zwillinger’s letter. Previously, Amazon has denied that its shoes are Allbirds knockoffs.

In his letter, Zwillinger offered to share the components it uses to manufacture its shoes with Amazon. Allbirds currently sells its materials, made from organic material like wool and trees, to over 100 other brands, according to Zwillinger.

„We want to give you the components that would make this shoe not just look like ours, but also match our approach to sustainability,“ Zwillinger wrote.

The letter builds on similar remarks that Zwillinger made during an interview with CNN’s Christiane Amanpour last week in which he called Amazon’s shoes „algorithmically inspired.“

Amazon is still selling its 206 Collective Wool Blend Sneakers, which strongly resemble Allbirds. Amazon’s shoes were initially listed at $35, but have increased to $45 in recent weeks.