- Your company is most certainly not allowed to break the NLRA. No company is.

- But your company can terminate your employment without cause whenever they like, as long as it's not over something that breaks the law, and as long as they pay the associated full severance.

- You talk about your salary. And given the vast majority of jobs aren't "my employer's so great, I get paid so well" but "there is so much inequality, let's talk about salaries so we can see how deep the rot goes", it's not going to be in a positive light.

- A short while later (definitely not immediately, your company's not a nice company, and it's going to take some time to make sure it has anything on you that they can legally fire you over that doesn't violate the NLBA) your company fires you, without reason, but with full severance.

- You challenge them to provide a reason

- Their lawyers point out they are under no obligation to provide you with a reason because they are complying with "termination without cause" legislation, and that if you think your dismissal was in violation of the law, you take it to court.

Now you have a problem, because now you're going to have to take them to court and prove that they only reason they could have fired you is because you talked about your salary. Can you afford that court case or is it cheaper to take the severance? We're not talking about a happy happy justice "laws work" world, we're talking about the real world, and specifically the real, nasty, world of shit paying US companies, where you aren't a valuable employee but are a disposable asset to be replaced by a cheaper alternative the moment you give them reason to do so, whether that reason is legal or not, because they know you can't afford the challenge, and they know they just need any reason for you to make the case that it was more likely because you talked about salaries than anything else.