The Diet has enacted a voting reform law that will trim the Lower House by 10 seats and rezone electoral districts to address a national vote weight disparity that has put the results of Japanese elections "in a state of unconstitutionality."
Enacted on Friday by a majority vote in the Upper House, the law calls for cutting six single-seat constituencies and four proportional representation seats from the more powerful House of Representatives, leaving it with 465 seats.
Since redefining electoral districts will require some time, the earliest an election can be held under the reformed system will be next year. Any Lower House poll called before then will be conducted under the current system, which the Supreme Court has criticized for years.
The change is intended to keep the vote weight disparity between the most populated and least populated single-seat constituencies below a ratio of 2-to-1. The Supreme Court has determined that exceeding this level is constitutionally problematic.
The single-seat constituencies to be cut are in Aomori, Iwate, Mie, Nara, Kumamoto and Kagoshima prefectures, while the four proportional representation seats are from blocs in the Tohoku, Hokuriku-Shinetsu, Kinki and Kyushu regions.
To better reflect local population sizes, the new law also calls for introducing a seat allocation method based on a formula that bears the name of John Quincy Adams, the sixth president of the United States, who is said to have proposed it.
But since the introduction of the Adams electoral method will be based on the results of the 2020 census and won't take place until 2022 or later, opponents who sought the immediate adoption of the Adams method remain critical: They say a court could still rule against elections conducted under the new law.