So it's okay if some people are allowed to abuse their positions by firing someone who essentially added a little footnote on one website in particular with a reminder as to what Federal law actually dictates?
That's my issue with that logic. We are all citizens first. Corporate shenanigans should never undermine civil rights. The right to organize and to do so at work, is protected, just as the right of a corporation to spew as much anti-unionization propaganda is protected. Period.
The employer will find any other excuse besides the blatantly illegal thing on which to pin the rationale for the firing. They just want to reap the benefit of the outcome (one less active organizer) without the hassle of being called to the carpet for a clear violation of labor law. That's how it works. It's all about how to get what you want while having an out to fall back on when someone calls you out. This is why legal departments exist. To ensure a jury in the event of getting called out will have to slog through every conceivable distraction before the company can be held accountable for their actions.
If someone makes an alert that management wishes to overrule, that seems like a really good reason to be able to revert commits, which I believe Google's version control system is able to do.
If they made a really bad mistake and you want to make sure they don't do it again, that seems like a really good reason to have their manager call them into a meeting.
If they made a really, really bad mistake, then perhaps there's formal disciplinary action, like a negative performance review or a docked bonus.
None of this seems like a reason to fire someone. Definitely none of this seems like a reason to drag them into a conference room and interrogate them to disclose the names of other people they're organizing with. That's what you would do if you were threatened by the content of the notification instead of unhappy with an abuse of process.