The Diet began an extraordinary session Friday following last month's upper house election, picking a senior Liberal Democratic Party lawmaker as new president of the chamber and a veteran lawmaker from the main opposition Democratic Party of Japan as his deputy.
The LDP, headed by Prime Minister Shinzo Abe, regained control of the chamber for the first time in six years following last month's House of Councillors election.
The 242-seat chamber chose 71-year-old Masaaki Yamazaki, a former deputy chair of the house, as new president in a unanimous vote, but in picking 77-year-old Azuma Koshiishi as his deputy, some mistakes occurred.
A total of three lawmakers cast two votes each, in a rare development that forced a second vote on Koshiishi.
Two of the three immediately came forward, explaining they had accidentally cast a ballot and an extra paper together. The third person is unknown.
Before the voting, all lawmakers were given a ballot paper for the president, another for the vice president, and an extra paper.
The erroneous voting did not affect the result of Koshiishi winning approval. But the LDP submitted to the house a motion to punish the two lawmakers -- Seiji Mataichi, acting representative of the small opposition Social Democratic Party, and an independent, Keiko Itokazu.
"That was an act of damaging confidence in parliament," Masashi Waki, LDP secretary general in the upper house, told reporters.
At the outset of the six-day Diet session, lawmakers also chose chairs of standing committees in the house, and they are not scheduled to deliberate on any bills during the session.
But tensions have also been growing amid heated criticism by opposition parties of Deputy Prime Minister Taro Aso, who triggered controversy this week at home and abroad by making remarks that appeared to consider Nazi Germany's changing of the Weimar Constitution as an example for Japan in revising its supreme law.
Aso, a former prime minister who currently doubles as finance minister, has already withdrawn the remarks, expressing regret he caused "misinterpretation" by holding up as an example the totalitarian government under Adolf Hitler during World War II.
But the opposition camp is increasingly calling for him to resign as a Diet member, urging the ruling bloc to make time to discuss the issue in a Diet committee.
On Friday, Aso ruled out stepping down as minister as well as lawmaker, while Chief Cabinet Secretary Yoshihide Suga supported him, stressing the government's view that the issue has been concluded following Aso's retraction.
Following the latest session, the Diet is expected to convene another extraordinary session in the fall where parties will mainly discuss the government's strategy for economic growth, including tax measures to encourage companies to boost capital spending.