Amazon has reportedly threatened to fire at least two employees who criticized the e-commerce giant’s record on the environment, telling them that they violated the company’s external communications rules.

The Washington Post reported Monday that an attorney for Amazon’s employee-relations group sent a letter to two workers who had previously spoken to the newspaper, warning them that future unauthorized communication could “result in formal corrective action, up to and including termination of your employment with Amazon.”

The two Amazon employees — Maren Costa and Jamie Kowalski — spoke to the Post in October, saying in a joint statement that the company is contributing to climate change due to its cloud computing business, which they claimed was helping oil and gas company exploration.

Costa told the newspaper that she will not be silenced.

“It’s our moral responsibility to speak up — regardless of Amazon’s attempt to censor us — especially when climate poses such an unprecedented threat to humanity,” she told the Post.

A third Amazon worker told the newspaper that she was called into a company meeting after posting to social media and speaking to news outlets about Amazon and the environment.

The Post noted that all three workers are members of Amazon Employees for Climate Justice, a group that is demanding that the company commit to being carbon neutral by 2030 and to ending cloud computing contracts associated with energy companies that engage in fossil fuel extraction.

An Amazon spokesperson said that the company’s external communication policy “is not news and we believe is similar to other companies.” The spokesperson added that employees are “encouraged to work within their teams” to suggest “improvements to how we operate.”

Amazon CEO Jeff Bezos has publicly spoken about his commitment to fighting climate change. In September, he unveiled a sweeping plan that commits the online retailer to meet the goals of the Paris Climate Agreement ten years early.

“We’re done being in the middle of the herd on this issue — we’ve decided to use our size and scale to make a difference,” Bezos said in announcing the plan.

But rank-and-file Amazon employees have been agitating publicly against the company and its environmental record, claiming that Amazon is aiding fossil fuel companies and therefore contributing to the climate change problem.

In September, a group of Amazon workers along with those from Google and Microsoft walked off the job as part of a global climate strike.

The Post reported that Amazon has a social media policy that allows employees to post messages so long as they don’t disclose confidential business information. They are also supposed to note that their views don’t reflect those of the company.

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