At least two Amazon employees pushing for the company to take stronger action on climate change received notices from their employer warning that they could be fired for speaking to the press. The workers are part of the group Amazon Employees for Climate Justice, which published a letter last April calling on the e-commerce giant to adopt a company-wide plan to address climate change. The letter was signed by more than 8,700 employees.

The Washington Post reported on January 2nd that at least two employees who made comments to media criticizing Amazon’s environmental impact in October were told that they violated the company’s communications policy. One of those employees, Maren Costa, a user experience principal designer at Amazon, was active in Amazon Employees for Climate Justice and had spoken to the media before.

Things heated up in September when Amazon Employees for Climate Justice organized a walkout to pressure Amazon to eliminate its greenhouse gas emissions by 2030, among other demands. One day before the walkout, Amazon announced a “Climate Pledge” to reach net-zero carbon emissions by 2040. However, the company explicitly disagreed with another demand made by employees who wanted Amazon Web Services to end its contracts with fossil fuel companies. “We are going to work very hard to make sure that, as they transition, they have the best tools possible,” CEO Jeff Bezos said at the time. “To ask oil and energy companies to do this transition with bad tools is not a good idea.”

That’s what Costa commented on in The Washington Post in October, telling the newspaper that “Amazon’s position is based on false premises and distracts from the fact that Amazon wants to profit in businesses that are directly contributing to climate catastrophe.”

Soon after she was quoted by the Post, Costa was called into a meeting with human resources. She later received a letter and email from an attorney in the company’s employee relations group warning that breaking the communications policy again could result in her losing her job.

“It was scary to be called into a meeting like that, and then to be given a follow-up email saying that if I continued to speak up, I could be fired,” Costa told the Post in an email. “But I spoke up because I’m terrified by the harm the climate crisis is already causing, and I fear for my children’s future,” she said.

A spokesperson for Amazon told The Verge in an email, “As with any company policy, employees may receive a notification from our HR team if we learn of an instance where a policy is not being followed.”

Costa spoke out again in a press release yesterday: “Now is a time when we need to have Communications policies that let us speak honestly about our company’s role in the climate crisis. This is not the time to shoot the messengers. This is not the time to silence those who are speaking out.”

People who work for Google and Microsoft have made similar demands as their peers at Amazon and also walked off the job in September.