New York (CNN Business)Layoffs for about 4,000 salaried staff at General Motors are due to start Monday. The layoffs are part of a 15% reduction in white collar jobs in North America that the automaker first announced back in November. At the same time, it announced plans to close four US plants as well as a fifth in Canada. While those plants, which include about 6,000 hourly jobs, have yet to close, GM is moving ahead with the salaried staff reductions, a GM spokesman confirmed Friday. The timing of the layoffs was first reported by the Detroit News. The company...