Sarah Tew/CNET

More than 350 Amazon employees defied the company's corporate communications policy on Sunday, with a Medium post criticizing its contribution to climate change. The move comes weeks after workers alleged that Amazon threatened to fire them for speaking out.

The post from Amazon Employees for Climate Justice, an internal activist group that started in late 2018, includes comments from 357 named workers who slammed its links with the oil and gas industry, collaboration with US Immigration and Customs Enforcement and warehouse conditions. The Washington Post, a paper owned by Amazon boss Jeff Bezos, previously reported on the move.

On Monday, the group tweeted a video featuring employees saying some variation of the phrase "We will not be silenced" and seeking Amazon's support for its workers "taking leadership on the most important issue of our lifetime."

1/ Hundreds of us decided to stand up to our employer, Amazon. We are scared. But we decided we couldn’t live with ourselves if we let a policy silence us in the face of an issue of such moral gravity like the climate crisis. #AMZNSpeakOut pic.twitter.com/zWIKku4LF6 — Amazon Employees For Climate Justice (@AMZNforClimate) January 27, 2020

"Every person who shared a statement had to decide for themselves that whatever the consequences, they needed to stand up for what they felt was right," said Victoria Liang, a software development engineer, in a release. "The climate crisis is just that urgent. We just couldn't be silenced by these policies on issues of such moral weight."

Now playing: Watch this: Jeff Bezos announces climate pledge

Several employees praised the plan to purchase 100,000 electric delivery vans, but noted that Bezos' September 2019 pledge to make company carbon neutral by 2040 seems unambitious compared to Microsoft's recent commitment to be carbon negative by 2030.

The group's push won support from Democratic presidential primary candidate Bernie Sanders.

"I stand with these Amazon employees who are courageously speaking out," he tweeted Monday. "They are telling Jeff Bezos to end his hypocrisy: You cannot call your corporation a 'leader' on climate change while partnering with ExxonMobil and BP to extract more fossil fuels."

I stand with these Amazon employees who are courageously speaking out. They are telling Jeff Bezos to end his hypocrisy: You cannot call your corporation a "leader" on climate change while partnering with ExxonMobil and BP to extract more fossil fuels. https://t.co/sStmoHqRFq — Bernie Sanders (@SenSanders) January 27, 2020

Amazon -- which employs around 750,000 people in total -- responded to the post by highlighting its passion about issues including climate change.

"Our 'Positions' page makes this clear and outlines what we're doing about them," an Amazon spokesperson said in an emailed statement. "While all employees are welcome to engage constructively with any of the many teams inside Amazon that work on sustainability and other topics, we do enforce our external communications policy and will not allow employees to publicly disparage or misrepresent the company or the hard work of their colleagues who are developing solutions to these hard problems."

Amazon Employees for Climate Justice is among several movements that have grown within the company. Similar groups have appeared in Microsoft, Google and other major tech companies, indicating an increase in activism within the industry.

First published on Jan. 28 at 4:16 a.m. PT.

Updated at 4:45 a.m. PT: Adds more detail. Updated at 4:55 a.m. PT: Adds Amazon statement.

Updated on Jan. 29 at 4:12 a.m. PT: Adds group's video and notes Sanders' support.