Tim Bray, a vice president and top engineer at Amazon Web Services, has quit the internet giant, citing in an open letter its “chickenshit” decision to fire whistleblowers raising concerns about safety for warehouse workers during the coronavirus pandemic.

Amazon’s treatment of its warehouse workers has garnered increasing scrutiny amid COVID-19 as a reliance on online shopping has spiked amid ongoing health concerns. A report in The Washington Post from mid-April stated that at least 74 Amazon warehouses and delivery facilities in the U.S. had reported cases of COVID-19.

In his letter, Bray cited Amazon’s decision to fire warehouse workers like Bashar Mohammed and Chris Smalls, who tried to organize workers over safety issues, and were reportedly let go for violating the company’s quarantine and social distancing rules. In a leaked internal memo, Amazon leadership discussed trying to smear Smalls in the press as “not smart or articulate” and make him “the face of the entire union/organizing movement.”

Bray also mentioned tech employees Emily Cunningham and Maren Costa, two leaders of the Amazon Employees for Climate Justice movement, who publicly denounced warehouse conditions as unsafe during COVID-19 and helped organize a video call with warehouse employees around the world. They were reportedly dismissed for violating Amazon’s internal policies. Bray called Amazon’s justification “laughable” and added of Cunningham and Costa, “it was clear to any reasonable observer that they were turfed for whistleblowing.”

“Firing whistleblowers isn’t just a side-effect of macroeconomic forces, nor is it intrinsic to the function of free markets,” Bray said. “It’s evidence of a vein of toxicity running through the company culture. I choose neither to serve nor drink that poison.”

As a VP at Amazon Web Services — the high-profile cloud computing wing of the company — Bray said he tried to raise his own concerns through the proper channels, but added that he ultimately felt that “remaining an Amazon VP would have meant, in effect, singing off on actions I despised. So I resigned.” He also acknowledged — somewhat cautiously — Amazon’s attempts to improve worker safety, and said that while he’d spoken with people he trusted about these efforts, “let’s grant that you don’t turn a supertanker on a dime.”

Bray continued: “But I believe the worker testimony too. And at the end of the day, the big problem isn’t the specifics of COVID-19 response. It’s that Amazon treats the humans in the warehouses as fungible units of pick-and-pack potential. Only that’s not just Amazon, it’s how 21st-century capitalism is done… If we don’t like certain things Amazon is doing, we need to put legal guardrails in place to stop those things. We don’t need to invent anything new; a combination of antitrust and living-wage and worker-empowerment legislation, rigorously enforced, offers a clear path forward.”