More than 3,200 people have asked prosecutors to investigate a dozen former and current executives of Kansai Electric Power Company who received cash and gifts from a local government official.
A citizens' group filed the criminal complaint at the Osaka District Public Prosecutors' Office on Friday to investigate the 12 people.
They include Kansai Electric's former chairman, Makoto Yagi, and its president, Shigeki Iwane.
The 12 have admitted that they received cash and gifts from Eiji Moriyama, a former deputy mayor of Takahama Town, Fukui Prefecture, who died earlier this year.
The town hosts one of the utility's nuclear power plants.
The group alleges that Yagi, Iwane and two others caused damage to the company by awarding contracts with padded costs to a construction firm that employed Moriyama as an advisor.
It says they are suspected of aggravated breach of trust and graft.
Kansai Electric has launched an independent panel to look into the scandal. But the group wants the law enforcement authorities to find out what happened.
The group hoped to solicit 1,000 people to join its action, but 3,272 signed up.
Lawyer Hiroyuki Kawai says the sheer number of people who have joined the complaint shows the depth of the public's anger, and prosecutors should get to the bottom of the scandal.