Wow, I hope President Obama is reading James Kwak and Zephyr Teachout. Here is a great post on Baseline Scenario by James Kwak discussing how anti-trust laws might be applied to break up the big banks. A great quote from Teachout is "Economies of scale [of large corporations] might work all too well when it comes to influencing government."
How would this argument be made against other corporations that aren't, at least at the moment, so threatening such as Walmart or IBM? Some large corporations don't consider themselves as "US Companies" - this is not a new problem. Compliance with any new anti-trust laws will need to be a precondition to doing business in the US market, regardless of loop-holes on "nationality" based on esoteric criteria.