The United Auto Workers chose Fiat Chrysler Automobiles NV, the weakest of the Detroit Three carmakers, as the surprise target for negotiating a new four-year labor agreement, Bloomberg News reported yesterday. The choice bucks the union’s tradition of choosing the strongest company among Fiat Chrysler, General Motors Co. or Ford Motor Co. to extract the best terms for its 140,000 members, a process known as pattern bargaining. This year’s dynamics were unusual because Fiat Chrysler laid bare its weaknesses and has been vocal about the need for a merger partner. The UAW’s contracts with Fiat Chrysler’s North American unit, GM and Ford are set to expire at midnight tonight in Detroit. The union will focus on Fiat Chrysler while working with all three companies toward a collective bargaining agreement, UAW President Dennis Williams said yesterday.