SAN FRANCISCO/DETROIT (Reuters) - The United Automobile Workers union on Friday said it had been approached by workers at Tesla Inc's Fremont, California, assembly plant, rejecting a charge by the chief executive of the luxury electric car maker that a worker who publicly criticized the company was on the UAW payroll. The nascent move to organize at Tesla's factory shines an unwelcome spotlight on allegations of long hours, mandatory overtime and preventable injuries at a time when Tesla is accelerating production to meet ambitious targets. The worker, 43-year-old Jose Moran, said on Friday his goal was to unionize at the factory where he has worked since 2012, often pulling 12-hour days, six days a week.