Do you have a link for that claim? Doesn't sound NAFTA friendly...
I had a customs license that listed all the tariffs and other than jewlery and furs the top duty charged by the US was 2%.
I also used to smuggle freon to a fishing fleet in Guymas and it was confiscated by the comandante, I called the fleet owner and he came down, paid a small bribe, loaded the 1,200# of freon and we went to dinner.
even food items in Baja that were canned in the US, like tomatoes, are 50% more expense than in California because of the 50% tariff.