I think that's actually the effect of anti-trust/anti-monopoly laws.
There's a point where companies get "too big to fail"/"too big to jail" and have outsize effect on the country (especially if the country is stupid enough to pass a Citizens United law that explicitly allows them to do this). Anti-trust laws are the main way that the government tries to prevent this, and haven't really been used since Reaganomics decided that big == efficient. Until recently.
Passing a law that companies cannot exceed a certain size (market cap as a percentage of GDP, I guess?) would probably be a simpler way of achieving this. Though, obviously, the accounting profession would roll up its collective sleeves and declare "challenge accepted".
With only a passing knowledge of the field, I'm aware that the standard of monopolistic effect varies between the EU and US (neither specifically uses financial size as the standard). In the EU it's about whether there is sufficient competition in the market, whereas in the US it's about whether the price is sufficiently competitive.
In US it's basically "whether there's harm to the consumer", which is so nebulous that large monopolists can often successfully argue that their abusive practices are a net benefit (usually by arguing that prices are lower).
There's a point where companies get "too big to fail"/"too big to jail" and have outsize effect on the country (especially if the country is stupid enough to pass a Citizens United law that explicitly allows them to do this). Anti-trust laws are the main way that the government tries to prevent this, and haven't really been used since Reaganomics decided that big == efficient. Until recently.
Passing a law that companies cannot exceed a certain size (market cap as a percentage of GDP, I guess?) would probably be a simpler way of achieving this. Though, obviously, the accounting profession would roll up its collective sleeves and declare "challenge accepted".