Amazon has threatened to fire at least two employees after they spoke out about environmental damage being caused by the company, a collective of its workers has claimed.

The e-commerce giant told Maren Costa and Jamie Kowalski that they were breaking staff rules by making public comments relating to the firm.

The pair are members of Amazon Employees for Climate Justice, a group of mainly tech and design staff who have accused boss Jeff Bezos of running a business model that “directly contributes to the climate catastrophe”.

In statements published online, the collective demanded the company achieve zero carbon emissions by 2030, stop working with fossil fuel companies, and end funding for politicians who deny climate change is happening.

It said members “believe it’s our responsibility to ensure our business models don’t contribute to the climate crisis”.

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But the group has now accused bosses of using “intimidation tactics” after HR and legal teams contacted Ms Costa, a designer, and Mr Kowalski, a software engineer, to warn them they were in breach of company policies.

Both were called to meetings and then sent follow-up emails raising the possibility of contract termination if they continued to speak out, the group said in a statement online.

“This is not the time to shoot the messengers,” said Ms Costa. “This is not the time to silence those who are speaking out.”

She added: “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.”

Amazon has since said its rules relating to staff making public statements were not new and in line with the policies of other firms.

But it added: “We recently updated the policy and related approval process to make it easier for employees to participate in external activities such as speeches, media interviews, and use of the company’s logo.”

It continued: “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.”