I was recently promoted, and received an insulting low-ball salary offer for the new position. I know it was low because I asked my coworkers at the position level I was promoted to what they made, and they told me. A colleague in HR also confirmed what the salary band for the position was. Based on my experience level and that of my coworkers, the salary is way too low and they're trying to underpay me.
I made it pretty clear that I found the salary offer insulting and that it was making me consider other options. When I asked to negotiate my salary, the VP of my department agreed to meet with me to discuss. I told them my rationale for asking higher and how I had learned pay range from my colleagues, and he responded by saying that I shouldn't be discussing pay with my coworkers and that they were now hesitant to approve the final push through of my promotion. They said I should have gone directly to them first to discuss, as that was more appropriate. (They also said they were unwilling to budge on the offer, so I'm planning to leave anyway.)
I view this as retaliatory behavior, but it happened on a phone call. My boss was present on the call and could corroborate that conversation if it came to anything, but does it seem like I have a case under NLRB? The only thing I have in writing is in an email I received confirming a cost of living increase I got a few months ago, with “PERSONAL AND CONFIDENTIAL” plastered all over the email.