By Daina Beth Solomon MEXICO CITY (Reuters) – A Mexican union said on Monday it will ask the U.S. government to investigate a Panasonic plant for alleged worker rights abuses, the latest in a series of disputes seeking to leverage a new trade deal to improve workplace conditions in Mexico. In a petition to U.S. labor officials, to be filed on Monday and shared with Reuters, Mexican union SNITIS said a Panasonic plant in the border city of Reynosa violated the 2020 United States-Mexico-Canada Agreement (USMCA) by signing a union contract behind workers’ backs and firing several dozen employees who protested.