General Motors is building up stocks of cars and light trucks in the US in what are thought to be preparations for a possible strike in the autumn as it heads for a showdown with its unions, the Financial Times (FT) reported on its website. The report said Detroit’s Big Three, GM, Ford and DaimlerChrysler, start negotiating a new, three-year labour contract with the United Autoworkers Union on July 18 with a contract expected to be finalised by mid-September.