Two groups of lawyers filed suits Monday with high courts seeking to nullify the results of Sunday's election because of the Diet's perceived failure to correct disparities in the weight of votes among districts.
A group led by Hidetoshi Masunaga submitted suits to the Okayama and Matsue branches of the Hiroshima High Court, as well as the Akita branch of the Sendai High Court, and planned to file further suits later Monday with high courts across the nation.
The other group, headed by Kuniaki Yamaguchi, filed a suit with the Hiroshima High Court and intends to lodge suits with the high courts in Tokyo and Osaka by the end of the month.
It would be the first time such suits have covered all 295 single-seat districts in the nation.
On Sunday, the vote-weight gap stood at 2.13 between the Tokyo No. 1 constituency, with 492,025 eligible voters, and the Miyagi No. 5 district, with 231,081, government data showed.
In November 2013, the Supreme Court ruled that disparities of up to 2.43 times in the December 2012 Lower House election were "in a state of unconstitutionality." But it stopped short of declaring the result invalid, noting the Diet had reduced the number of single-seat constituencies to 295 from 300.
Attorney Tetsuya Kanao told a news conference in Hiroshima the electoral system should be "drastically reviewed" because the elimination of a mere five districts was "a drop in the ocean."
"We cannot overlook the Diet's negligence," he said.
Shintaro Kagawa, of the group that filed the suit with the Okayama branch, called on the Hiroshima High Court to "meet the Constitution's provision that elections must be conducted in accordance with the population" and said all vote-weight disparities must be eliminated.
The Public Offices Election Law stipulates that lawsuits regarding the validity of national election results must be initially tried at high courts.