Groups of lawyers and voters have filed lawsuits across Japan, demanding that the results of Sunday's Upper House election be nullified due to disparities in the value of votes.
One of the groups filed a suit with the Tokyo High Court on Monday afternoon.
The value of votes cast in the least populated electoral districts was about three times that of those in the most populated districts.
The plaintiffs and another group say the disparity violates the country's Constitution, which guarantees that votes have equal value.
The two groups have filed similar suits with high courts and their branches across the nation.
In the previous Upper House race three years ago, the maximum vote disparity was 3.08 times.
The Supreme Court ruled in 2017 that such a disparity is not unconstitutional. But it acknowledged the need to narrow the gap in the run-up to the next election.
Last year, the Diet revised the public offices election law to increase the number of seats up for grabs in Saitama from three to four. The number of voters per lawmaker had been the highest of any district.
Lawyer Makoto Ito of one of the groups said he wants the value of votes to be equal in all districts across the nation.