Jeff Bezos, founder and chief executive officer of Amazon.com Inc., speaks at the National Press Club in Washington, D.C., on Thursday, Sept. 19, 2019.

In a statement posted to Twitter on Thursday, Amazon Employees for Climate Justice said that several employees were contacted by legal and human resources representatives, who said they were in violation of the company's external communications policy.

A group of Amazon employees say the company has threatened to fire two workers for speaking out against the company's environmental policies.

Two employees were told their roles would be terminated if they continued to speak out about Amazon's business, a spokesperson for the group told CNBC.

Maren Costa, a user experience designer, was one of the employees Amazon threatened to fire. In the statement, Costa said: "This is not the time to shoot the messengers. This is not the time to silence those who are speaking out."

https://twitter.com/AMZNforClimate/status/1212777102270820353?s=20

Amazon also threatened to terminate Jamie Kowalski, a software development engineer, according to The Washington Post, which first reported the news on Thursday. Kowalski and Costa said they received letters from one of Amazon's lawyers after speaking out publicly in October, the Post reported.

In the statement, the employee group claimed that Amazon changed its policy in September and that the updated policy "requires employees to seek prior approval to speak about Amazon in any public forum while identified as an employee."

However, Jaci Anderson, an Amazon spokesperson, said the company's communications policy isn't new. In September, Amazon actually tried to make it easier for employees to speak out by adding a form on an internal website where employees could seek approval; prior to that, they had to get direct approval from a senior vice president. She added that employees are "encouraged to work within their teams" and can suggest "improvements to how we operate through those internal channels."