A group of 10 people working as freelance delivery drivers for Amazon.com Inc.’s Japan unit have unionized and handed over a letter to the online shopping giant’s Tokyo headquarters demanding that their poor working conditions be corrected, union members said Monday. The union claimed that, despite working as freelance drivers, Amazon Japan G.K. effectively controls their work hours by sending delivery instructions via smartphones and that outsourcing of delivery operations is a way to avoid signing labor contracts. Lawyers and supporters of the group said this is the first time Amazon deliver…