To cast a vote, MPs have to insert an official identification card into a balloting slot. The scandal broke after certain senators and MPs pointed out that some Pheu Thai MPs were not present but had been able to vote by surrendering their IDs.
Somsak said he doubted if the scandal would void the vote on the charter amendment bill, arguing the majority support for the bill should outpace a few invalid ballots.
He said the opposition had the right to petition the Constitution Court for a judicial review on the issue but he did not think the court battle would alter the passage of the bill.
The second reading of the bill is taking place over eight days, he said, revealing that the debate will adjourn for the weekend and resume on Monday.
Prime Minister Yingluck Shinawatra said all sides should check the facts before drawing a conclusion on the scandal.
If MPs unwittingly made a mistake, they should be cautioned, Yingluck said, adding that in the case of a clear violation of House rules, the Pheu Thai Party will punish them.
Pheu Thai MP Samart Kaewmechai said penalties for violating House rules ranged from a caution to denying the nomination for re-election.
Pheu Thai MP Jirayu Huangsub said he was willing to submit his resignation if the allegations were true.
He said that the voting scandal was a fabricated story because the Pheu Thai MPs involved had surrendered their IDs.