It's not clear to me why the open letter authors are protected under the NRLB at all. They seemed to be criticizing the boss, which is not illegal, but not really a labor action either?
There was a list of demands of the executives. But yeah, there was no call for a labor action. If anything, they were demanding the company take more drastic steps to start removing employees for bad behavior.
> SpaceX’s current systems and culture do not live up to its stated values, as many employees continue to experience unequal enforcement of our oft-repeated “No Asshole” and “Zero Tolerance” policies. This must change. As a starting point, we are putting forth the following categories of action items, the specifics of which we would like to discuss in person with the executive team within a month:
Since they apparently had a "no asshole" policy it would seem that if anything, calling your boss an asshole is officially endorsed.
Not deserving to be fired is not the same as being federally protected from being fired. NRLB says that being fired for what they did is illegal, and that's hard for me to square with how I understand labor law.