The Japanese Trade Union Confederation — better known as Rengo — has a long history of backing opposition parties. So in April, as the country began to prepare for the summer Upper House election, it came as a shock to many observers when the head of Rengo, Tomoko Yoshino, attended a meeting with the ruling Liberal Democratic Party to discuss labor issues.

The meeting added fuel to a fire that started in January, when Rengo leaders said the organization would not specify which political party or parties it would back in the election, even though two of the main opposition parties, the Constitutional Democratic Party and the Democratic Party for the People, are heavily reliant on votes from Rengo’s membership. Rengo has also said it will not back any candidates affiliated with the Japanese Communist Party.

Yoshino played down her meeting with senior LDP officials, brushing aside concern that Rengo would switch its support to the ruling party. But Taro Aso, the LDP's vice president, welcomed Yoshino’s efforts to meet with the ruling party on April 18. About a month before that, she attended a dinner with Aso, prompting him to observe that the relationship between the LDP and Rengo had evolved to the point where the two of them could drink sake together.