Amazon is very clear when you're hired that you're not allowed to represent the company or it's positions on social media or anywhere publicly without getting permission.
You can agree or disagree with that policy, but it's not new. Source: first heard of this policy when I was hired at Amazon in 2007.
>>influx+(OP)
The policy could also be in violation of law. Hard to see without looking at the policy and also without looking at the substance of the comments. But there are federal laws protecting certain worker activity and a policy doesn't overrule that.