The new president of the United Auto Workers gave his strongest warning yet Friday that the union is preparing for strikes against Detroit’s three automakers. In a Facebook Live appearance, Shawn Fain said the union is in a strong position to make major gains in talks with Stellantis, Ford and General Motors. But he said those gains will happen only if members get organized and are ready to strike. Fain repeated the union’s goals of winning back cost-of-living pay raises and pensions, general pay raises and elimination of tiers of workers who are paid different wages. The union also wants to represent workers at joint-venture electric vehicle battery plants. GM and Ford declined comment and a message was left for Stellantis. Contracts with the automakers expire Sept. 14.