Even saying that is against the law. The NLRB can't really punish the company much but, especially if you get proof of that in writing or in a recording, you can report it to the NLRB and at least scare them/humiliate the company by making them deal with an investigation. Potentially they could be forced to send emails/post notices/personally text employees telling them they have the right to discuss wages. If you talk about wages and they fire you for it and you have a paper trail of proof they'll end up having to give you backpay.