Mexico’s Economy Secretary, Graciela Marquez Colin, has formally requested an exemption from U.S. section 232 duties on steel and aluminum. That could be a sign that the tariffs are becoming a sticking point for Mexican ratification of the U.S.-Mexico-Canada Agreement alongside the need to implement labor reforms. The tariffs have in any event not cut Mexico’s steel and aluminum exports to the U.S. They climbed 10.9% year over year in the three months to Feb. 28 to reach $3.56 billion. That was due to a 112.4% surge in shipments by ArcelorMittal as well as increased exports by Ternium. B...