This has been the policy at every company I've worked for since the 90's. It's usually in the employee handbook, and at a couple of places I had to sign a separate paper acknowledging it.
Amazingly, several of those companies were news organizations. It's usually the first indication that a company is more interested in its stock price than doing the right thing.
But no one changes the policies until the NLRB requires them to after losing a case, even an easy case. Sometimes all they do is write "except where allowed by law" into the policy, then hope workers don't know what their rights are.