Ah, but perhaps now I see your point. Congress could arguably require a corporation to be federally chartered as a condition of operating in interstate commerce. It could then put whatever conditions it wanted on that charter.[1] (States could do this, too, but the race-to-the-bottom concern probably prevents it).

I think that would fail an equal-protection or privileges-and-immunities test under Citizens United (with the current Nine, anyway), but it's a thought.


[1] For instance, "A corporation chartered under this Act may sue and be sued in any State or Federal Court otherwise having jurisdiction, and may hold property in its own name, but is not a "person" within the meaning of any provision of the United States Constitution."