Upper House member Tatsuo Tomobe filed an objection Friday against a Supreme Court ruling upholding his 10-year prison term for fraud, his lawyers said.
The top court has never reversed or withdrawn a ruling following the filing of a petition, other than in cases where a defendant has died, or for technical reasons.
If the Supreme Court rejects Tomobe's motion, the 10-year sentence will be finalized and Tomobe, 72, will lose his Upper House seat in line with the Diet Law and the Public Offices Election Law.
The Supreme Court rejected Tomobe's appeal against a Tokyo High Court ruling on Dec. 20 that upheld the lower court-imposed sentence.
The lower court had ruled that Tomobe swindled 660 million yen from 35 people through an investment scheme run by Orange Kyosai, a mutual aid society under his control, from June 1994 through November 1996.
Tomobe has repeatedly insisted that he never intended to defraud anybody and pledged to return the funds.
He refused to resign from the Diet even after an Upper House resolution in April 1997 called on him to give up his seat after he was arrested Jan. 29 the same year.