MEXICO CITY, June 4 (Reuters) – Late changes to a new trade deal reached by the United States, Mexico and Canada will make it harder for auto companies to meet requirements for the use of regional steel and aluminum, a local industry lobby said on Thursday. Not only must 75% of the work be done in North America, but 70% of the steel and aluminum in a vehicle must also be purchased by North American manufacturers. A last-minute change in the law provided that steel had to be “melted and cast” in these countries to qualify for duty relief – although this important provision was introduced gradually over time. This is because many steel products had circumvented Section 232 tariffs of 2018 by shipping to Mexico, following the granting of a 232-duty exemption to Mexico earlier this year. . . .