GM requires suppliers to have a certain percentage of the parts made in a low-cost labor country.
Nissan, and Chrysler are perfectly content with local suppliers as long as the price is low. (However, they have other strategies to lower prices...) I don't know about Ford.
Toyota has gone to global supply pricing. Therefore, they don't care where the part comes from, but if it is cheaper in Mexico than it is in the US, they will require that US company to match the price that they can get it for from Mexico. Honda is moving towards this, but they certainly aren't there yet.