A large and increasing component of Canada's vehicle manufacturing industry is represented by companies like Honda and Hyundai that assemble vehicles in Canada to be sold throughout North America using a mixture of components manufactured in Canada and abroad.  

Provided that the Canadian (and US or Mexican) content equals or exceeds a portion of a typical vehicle's total for a vehicle specified under NAFTA, then the vehicle can be imported and sold in the US or Mexico.  It is the specified proportions that the US wishes to further restrict and this could make the attraction to foreign manufacturers of manufacturing in Canada deminish.