Nothing besides maintaining the illusion of free trade stops the US government from singling out a specific company for special restrictions. They already did so to BYD and CRRC in 2021, even though both companies have US factories.

The country of manufacture is irrelevant to the US government’s ability to impose restrictions on the sale of new vehicles within their borders. Chinese manufacturers could completely own the Mexican market and still have no presence in the US if a law is passed that says they’re not allowed.