The All-Japan Teachers' Union is the largest and oldest labor union of teachers and school staff in the country. It was founded on Auguest 8th, 1947 when three existing teaching organizations were consolidated

1. The union holds a critical stance against some issues of the conservative Liberal Democratic Party such as "Kimi ga Yo" (the new post WWII national anthem of Japan), the Flag of Japan, and for the LDP's avocation of the screening of history books2.

This organization is brought up in Rowing the Eternal Sea, a book by Oiwa Keibo during Ogata Masato's account of his growing up and moving to Kumamoto City after graduating from Junior High. 

Sources and Further Reading:

1http://www.jtu-net.or.jp/english/birth.html

2http://en.wikipedia.org/wiki/Japan_Teachers_Union