Branch profit tax applies if you have ECI only. If the US LLC is owned by an individual, then there is only tax on the ECI.
But if you have ECI and the US LLC is owned by a company and you transfer money out to the owner of the US LLC - then the branch profit tax applies. It's similar to a withholding tax.
Imagine that a UAE company owned a a US LLC that was operating a restaurant in Miami (no state taxes).
Scenario 1:
The US LLC is taxed as a corporation and makes a $1M profit. It pays the 21% CIT (hope I'm correct about the federal CIT rate). The remaining $790k are paid as a dividend to the parent company. There's no tax treaty, so a 30% withholding tax ($237k) applies. Only $553k can be paid out to the UAE parent company.
Scenario 2:
The US LLC is taxed as a disregarded entity (tax-transparent) and makes a $1M profit. There's obviously ECI (it's a restaurant), so the profit is subject to the same 21% CIT. But except for the ECI, it's tax transparent, so there are no dividends to pay out, so withholding tax on dividends doesn't apply. Without a branch profit tax, the after-tax profit of $790k can be transferred to the UAE parent company without any additional tax withholding.
That's what they wanted to fix because scenario 2 suddenly came with a massive tax advantage. So the branch profit tax was introduced, which simply puts the same withholding tax (additional 30% tax) on any money that is transferred out to the parent company, like a dividend. It's not a dividend though, that's why they call it the "dividend-equivalent amount".
So if you have ECI, it's a double whammy situation if the US LLC is owned by a company instead of an individual.
Just google it, there's a lot of info about it, e.g. this:
https://klasing-associates.com/question/branch-profits-tax/
However, there's also at least one positive with a company owning the US LLC: You can avoid the US estate tax.
If you die and you're the direct owner of the US LLC, then there would be US estate tax, at least on all US assets. I'm not sure if the value of the LLC itself would also fall under that.
If you die as the owner of the foreign company owning the US LLC, then the US LLC wouldn't be impacted at all.
Yes, that's the theory. And I've heard that it works perfectly fine like this for a lot of people.
However, if you have US business clients, they only see a US company. And they may send a form 1099 (if I remember correctly), because that's what they would have to do for a US supplier.
They will send a copy to the IRS and say "This US company is doing business for us, a US client". It's not your client's job to assess your tax status. You're a US supplier as far as they are concerned.
From what I understood, the purpose of this is to make it harder to evade taxes.
Basically your client reports your income to the IRS for you "We paid this US company $50k for their work".
Then the IRS will notice "So this US company earned $50k from this US client.... Why didn't they pay any taxes?" (Note that the company being owned by a non-resident alien doesn't automatically mean there was no ECI, as in scenario 2 above.)
So now the IRS may come looking for that tax. Or, to put it simply, they may simply assume/claim that there was ECI and then you would have to fight them about it.
And I guess in states like California, the IRS may be extra aggressive.
Yes, it sounded weird for me as well, but that's what both a very reputable (=expensive) US tax lawyer and also a CPA told me. They said it might make more sense to use the US LLC only to market to US clients and then bill from a foreign company (and not the same company that owns the US LLC).