Lower House member Takeshi Tokuda, whose elder sister is on trial on suspicion of illegally helping his election campaign in 2012 by providing cash to employees of Tokushukai, Japan's largest hospital chain, resigned from the Diet on Monday.

Tokuda, 42, would have to give up his Lower House seat anyway under the so-called guilt-by-association rules of the Public Offices Election Law if his sister, Michiyo Stern, who played a key role in his election campaign, receives a prison sentence, suspended or otherwise. Her ruling is set to be handed down on March 5.

Tokuda hopes to get leniency by resigning before Stern is sentenced, a senior member of the Liberal Democratic Party said. If his resignation is accepted, a Lower House by-election will be held on April 27 in the No. 2 single-seat constituency of Kagoshima Prefecture.