It's an issue involving third parties if the third party colluded. If there was any communication between Amazon and Google in this matter, that would be a problem.
The NLRB has recently been deciding cases involving employee criticism of employers in social media.[1] "The focus of
many of these recent rulings has been the protection of the right
of employees to communicate with their coworkers about their
terms and conditions of employment. Indeed, the NLRB has
increasingly defined the contours of this right expansively." There are lawyers who take on such cases.[2]
Neither of those address third parties. They both involve relations between employers and employees. Even if Amazon did somehow convince Google to take the site down, there are plenty of other avenues for employees to communicate. You would have a very hard time selling this in court.
The NLRB has recently been deciding cases involving employee criticism of employers in social media.[1] "The focus of many of these recent rulings has been the protection of the right of employees to communicate with their coworkers about their terms and conditions of employment. Indeed, the NLRB has increasingly defined the contours of this right expansively." There are lawyers who take on such cases.[2]
[1] http://www.postschell.com/site/files/post__schell__nlrb_arti... [2] http://employee-rights-atty.com/the-censor-he-has-a-face-and...