Sawet, who was involved in drafting the 2007 Constitution and is also the leader of the Thai Mai Thon political group, said those parliamentarians who had blocked Pita in the second round had failed to perform their duties.
He argued that any parliamentarian who had not voted for Pita was in breach of Article 157.
Pita's bid to be a candidate for prime minister in the second round of voting was foiled by 395 parliamentarians who rejected his renomination. They argued that Pita's candidature in the second round, after his failure in the first round, would be in breach of Parliamentary Rule No. 41, which forbids the resubmission of a motion that has already failed in the same session.
Sawet said legal action must be taken against those who opposed Pita's renomination.
Most of the senators and MPs have opposed Pita because of his party's stand on amending the lese majeste law, or Article 112 of the Criminal Code.
Sawet said that amending Article 112 is very normal and could be done.
He also urged Move Forward not to withdraw its policy to amend the law, as this was what the party had promised the people.
After failing to take the top job, Pita said that he would let Pheu Thai, the second-largest party in the coalition, take the lead in forming the government and would back its candidate for prime minister.
Sawet warned Pheu Thai not to join forces with pro-military parties, saying that doing so would be regarded as an act of deceiving the people. He said Pheu Thai's top PM candidate Paetongtarn Shinawatra had vowed before the election that her party would not form the government with the junta-backed parties.
Sawet believes that former premier Thaksin Shinawatra is the decision-maker behind Pheu Thai's every move.
Pheu Thai has come under fire and some groups have expressed their anger after the party held talks with pro-military parties like Bhumjaithai, Palang Pracharath, and United Thai Nation.
In response, Pheu Thai reiterated that it still has close ties with the other seven parties in the alliance and that the objective of the discussions was to entice more of their votes rather than establish the next government with them.
Sawet also said that the current Constitution, which he claimed was written by a dictatorship, was the problem now.
“There is no country in this world that allows appointed senators to take part in the vote to pick the country’s leader,” he said.