The USMCA was signed on November 30, 2018, by all three parties at the G20 summit in Buenos Aires, as had been planned the preceding months. However, continue disputes over labor rights, steel, and aluminum prevented ratification of this version of the agreement. Consequently, Canadian Deputy Prime Minister Chrystia Freeland, U.S. Trade Representative Robert Lightizer and Mexican Undersecretary for North America Jesus Seade formally signed a revised agreement on December 10, 2019, which was ratified by all three countries by March 13, 2020.