The ruling Liberal Democratic Party on Wednesday endorsed a bill proposed by four opposition parties to narrow vote disparities between constituencies in House of Councilors elections.
The five parties plan to submit the bill on Thursday to the Upper House. On the strength of their combined majority, they will seek to pass it through the chamber Friday before sending it to the House of Representatives.
The bill was proposed in June by the Japan Innovation Party, the Party for Future Generations, the Assembly to Energize Japan and the New Renaissance Party.
The bill would narrow the maximum vote value gap between the most and least populated constituencies to 2.97 times from 4.77 times in the previous Upper House election in July 2013, which the Supreme Court ruled last year was "in a state of unconstitutionality."
The bill would merge four two-seat prefectures — Tottori, Shimane, Tokushima and Kochi — into two two-seat constituencies and cut the number of seats from four to two each for Miyagi, Niigata and Nagano prefectures.
At the same time, it will increase the number of seats by two each for five other prefectures of Hokkaido, Tokyo, Aichi, Hyogo and Fukuoka, leaving the total number of Upper House seats unchanged at 242.
Earlier, the Democratic Party of Japan, the largest opposition group, and other parties submitted a separate electorate reform bill to narrow the vote value gap to 1.95-fold.