According to Amazon workers part of the Amazon Employees for Climate Justice group, the e-commerce giant has told its workers they were in violation of company policies, reports BBC.
This was after the group had called on their employer to do more to tackle climate change.
Amazon has said that its policy on employees making public comments is not new and covers all of the workers and not just the climate activists among them.
According to the group, they had been contacted by Amazon's legal and human resources teams and were questioned about the public comments they had made.
"Some workers then received follow-up emails threatening termination if they continue to speak about Amazon's business," they added.
Two were threatened with termination, a spokesperson for Amazon Employees for Climate Justice said, adding that a total of four were told in meetings that they were "in violation of the company's policies on workers speaking to the press and on social media."
Maren Costa, a user experience designer, was one of those threatened with termination after speaking to the Washington Post, according to a report by Bloomberg media.
Jaci Anderson, an Amazon spokesperson, said that employees are "encouraged to work within their teams," and that the company may suggest "improvements to how we operate through those internal channels."
The tech industry has seen a rising share of employee activism in the past couple of years.
Last year, Google workers had protested its company's bidding on military contracts, resulting in Alphabet's backing out of a US Defense Department drone program.
Similarly, employees at Microsoft Corp and Salesforce.com had pressured executives on their companies' dealings on controversial issues such as US immigration.