Under a Mexican labor reform that underpinned the new United States-Mexico-Canada Agreement (USMCA) trade deal, workers are now meant to be able to freely choose groups they feel will best fight for their interests.
A defeat for one of the most powerful unions in the country, the August vote was the first test of labor rules under an accord that replaced the 1994 North American Free Trade Agreement (NAFTA).
GM workers will be asked to choose from four unions aiming to win the contract, according to the document shared by the Mexican government on Friday.
One, SINTTIA, is an independent group that grew out of the efforts last year among workers to scrap their collective contract.
The union that previously held the Silao plant's collective contract will not attempt to win back its representation.
(Reporting by Daina Beth Solomon; Editing by David Gregorio)