Amidst a clamp-down on employee organizing that has spread throughout the tech industry, Amazon is being accused of attempting to silence workers who have publicly criticized the company’s environmental record.

Members of the activist group Amazon Employees for Climate Justice have been threatened with termination after speaking to the media, according to the group, which organized a 1,500 worker walkout last September. The white collar protest was the first of its kind in Amazon’s 25-year history.

“Four employees have been questioned and two have been threatened with termination if they continue speaking up about Amazon’s role in the climate crisis without seeking PR approval,” Maren Costa, a principal user experience designer and one of the threatened organizers at Amazon, told Motherboard.

On November 22, Costa received an email informing her that she had violated company policy, and that further infractions would “result in formal corrective action, up to and including termination of your employment with Amazon,” according to a letter reviewed by the Washington Post .

Amazon, which ships billions of packages each year and consumes enormous amounts of energy through its cloud computing services, stands out among the tech giants for its environmental record.

In early September, a day after Amazon Employees for Climate Justice announced their plans for a climate walkout, Amazon modified its policy for speaking to reporters by requiring its employees to receive approval from lower-level executives and provide “business justification” for speaking publicly. The company now requires employees to make a request on an intranet page—a process that can take up to two weeks, according to the Washington Post. Employees must also receive approval to post about their work on social media, Amazon told Motherboard.

Previously, workers were required to receive approval from senior vice presidents, a policy which Amazon did not typically enforce with activist employees.

“Our policy regarding external communications is not new and we believe is similar to other large companies,” an Amazon spokesperson told Motherboard. “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. 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.”

Still, organizers at Amazon say that the threats and policies changes will not hinder their efforts to challenge the company’s relationships with oil and gas companies, or its environmental record. “Despite the change to the communications policy, AECJ plans to continue pushing the company to do more to take action on the climate crisis,” Amazon Employees for Climate Justice (AECJ) said in a press release.

In April, more than 8,700 of the company’s 65,000 corporate employees signed onto a letter to Jeff Bezos demanding the company’s management resolve to eliminate its carbon footprint by 2030.

The Amazon organizers are also demanding that shipping giant cut ties with oil and gas companies, and end donations to climate-change denying lobbyists and politicians. Following news of the walkout, Jeff Bezos pledged to reduce the company’s carbon footprint by 2040, a decade earlier than the Paris climate accords. But Amazon activist employees said Bezos’ pledge falls short of their demands.

“Since announcing the Climate Pledge, Amazon continues to develop AWS products and services to accelerate oil and gas extraction and has not made a commitment to end funding of climate-denying politicians, lobbyists, and think tanks,” Amazon Employees for Climate Justice wrote in a press statement.