I do not believe this is how NLRB enforcement works.
Though if the US had sectoral bargaining like other countries it just wouldn't be an issue in the first place.
The answer for that is more regulation, stronger and more independent institutions that can rein those companies in. Not wishing thay companies magically become nicer.
I fully understand that that will not happen by itself.
What I'm advocating is changing the STRUCTURE in which they operate so that "becoming nicer" is prompted by the system. The current system fully expects only the primary goal of maximizing profit/value for the shareholders/owners, and minimal compliance with anything else.
This is despite the fact that EVERY corporation enjoys massive benefits of operating in a country that provides everything from transportation infrastructure, a reliable legal system, an educated workforce, to military protection of global shipping lanes.
It would help to embedding into the law the concept of corporate responsibility, by providing a cause of action for irresponsible corporate actions. Expecting the corporation to take care of the workers, and the environment. E.g., In Germany, it is required that workers have seats on the boards and workers have much greater rights.
The point is that the law is now, as you say, just [corps are expected to take care of only their shareholders] and [corps are subject to some regulation].
This system has been tried for nearly 250 years, and is obviously lacking.
I don't think iron-fisted regulation will provide a solution. That's already been tried, everyone got annoyed at the overhead, and it was backed off (see Reagan administration), and the corp destruction has ramped up ever since. It literally just becomes a higher priority to corps to do regulatory capture then.
We need to make the system harder to capture, spin a wider web. And that can be done by broadening the social and legal compact with corporations ('tho they'll fight like hell against it).
Those are interested ideas. But it begs the question: How to enforce compliance without regulation?
For example, corporations are strictly creatures of law; they exist IF and Only If, and in the form that the law allows, at the pleasure of the government.
So, rewrite the enabling laws to state specifically and explicitly that corporations have affirmative responsibilities not only to the shareholders, but also to their workers, the community, the nation, and the environment, etc.
That alone immediately gives cover to any executive or board taking action that benefits those entities and perhaps not so much the shareholders. So they have a defense against shareholder suits that seek to force action or compensation away from corporate responsibility. Plus, there would also be a cause of action from the other parties for failure to take care of their interests. Obviously, this could go too far in either direction, so it must be carefully written, but this is the general idea.
There are many other ways, but that's the idea, don't rely solely on regulation.
When the companies engage in the ordinary big-business practice of regulatory capture, absolutely nothing.
It is just treated as a game to be hacked. And hack it, they do.
Because according to your standards, companies don't need to treat everyone fairly (as a good citizen), but the govt must treat them fairly.
That's how earlier this week we saw headlines that Tesla employees in Buffalo NY were organizing a union drive. Then the very next day, we see headlines that Tesla has fired 10 workers, the ones organizing it.
It is illegal as hell, but they did it anyway. Why? Because Tesla knows that it'll take years for all the hearings to work their way through the courts, and the result will be a fine, which they can appeal, and delay further. Meanwhile, they figure the end cost will be less than having to deal with giving workers a fair deal. So, despite all the "excess govt regulation", the workers get exploited and screwed.
It is also how Norfolk rail donated to both Trump and the Ohio gov and had regulations eased, e.g., requiring fewer workers on trains and not needing to update their technology with "extra" brakes. And now we have an environmental disaster as a result. And those costs will be 'socialized' to the taxpayers and victims in the town, while the company keeps most of it's profits (it will not pay even a small fraction of the costs and it will be years from now).
So yeah, the govt structurally CAN NOT be as nimble as the companies, so the companies exploit that weakness. Great for them. Sucks for society.
I'm not saying they're all bad or evil, but this over-simplistic "shareholder value only" concept /structure is not good for a sustainable society or even for sustainable corporations.