They also called on the EC to conclude the investigation concerning small parties hired to compete in Sunday's election.

Thai Rak Thai deputy and caretaker Agriculture Minister Khun-ying Sudarat Keyuraphan, meanwhile, dared the commission to examine the party's "open" rallying tactics. If anyone had evidence that the incumbent Thai Rak Thai Party had assigned government officials to help woo votes for it, as alleged by some law lecturers, they should file complaints to the EC, she said.

Democrat Party deputy leader Jurin Laksanawisit, chair of a joint meeting of representatives from former opposition parties, said the EC's election rules might contain holes that would allow cheating, especially the use of rubber stamps. Although the EC issued letters to allow voters to make an X mark with a pen or rubber stamp, cheaters might still be able to use stamps to make the mark before the election, he said.

Chat Thai Party deputy leader Nikorn Chamnong said ballot boxes might be switched after the poll. With stamps it would be difficult to prove. Politician Sutham Rahong called for the use of stamps to stop.