Media expert Seree Wongmontha and former deputy prime minister Suthep Thaugsuban have denied allegations of defamation and election law violations.
The accusations relate to comments and social media posts made by the pair in the lead-up to last month's Bangkok governor election.
Former senator Ruangkrai Leekitwattana and voter Nicha Phaensomboon lodged separate complaints against Mr Seree with the Bangkok Election Commission (EC), while the Pheu Thai Party complained about Mr Suthep.
If either Mr Seree or Mr Suthep are found to have violated election laws by swaying voters, a new election could be called and the EC could consider criminal action against them.
They could also be forced to pay for the cost of re-running the poll.
The March 2 vote cost 176 million baht.
Both Mr Seree and Mr Suthep testified before the Bangkok EC yesterday.
Speaking after his testimony before a sub-committee probing the matter, Mr Seree said quotes attributed to him on the MThai.com website were published without his permission.
He said the website had published a statement he had posted on his personal Facebook page, but had edited it.
His original statement carried a disclaimer saying the opinions expressed were entirely his own and should not be used for any other purpose, he said.
In the Facebook post, Mr Seree made a case for voters not to choose Pheu Thai's Pongsapat Pongcharoen _ MR Sukhumbhand's primary opponent.
He said the statement was his own analysis of the election, and he had no intention to help MR Sukhumbhand, nor to defame Pol Gen Pongsapat.
"It's unfair to single me out from the many others who posted similar statements on their Facebook pages," he said.
Democrat Mr Suthep also defended himself against similar allegations before the panel.
He denied any wrongdoing, insisting he only discussed facts during the campaign and he had witnesses and documents to prove it.
The allegations against Mr Suthep stem from various comments he made during the Democrats' city election campaigning.
Speaking later, Mr Suthep said he was alleged to have falsely accused Pheu Thai of plotting to change the country's governance to a presidential system.
He is also accused of claiming ousted prime minister Thaksin Shinawatra and the red shirts were colluding in causing political unrest in which innocent people and state security workers were injured.
In addition, he said he was alleged to have falsely accused Thaksin of urging his supporters to vote for Pol Gen Pongsapat and said that Pol Gen Pongsapat was simply Thaksin's political nominee.