The embattled Election Commission (EC) is expected to face two potentially serious petitions on Tuesday with one calling for the nullification of the March 24 poll and the other demanding the impeachment of its seven members for alleged malfeasance in its handling of the election.

Srisuwan Janya, secretary-general of the Association for the Protection of the Constitution, will on Tuesday submit a petition to the National Anti-Corruption Commission (NACC) seeking the ouster of the EC members.

He said the petition accuses the commissioners of deliberately using their power in a way that breached the constitution.

If the NACC rules there are grounds to the allegations, the case will be forwarded to the Office of the Attorney-General for consideration. If the Supreme Court's Criminal Division for Holders of Political Positions accepts the case for trial, the EC members will have to suspend their duties, he said.

In the meantime, Ruangkrai Leekitwattana, a former member of the now-dissolved Thai Raksa Chart Party, said he will on Tuesday lodge a petition with the ombudsman asking it to examine questions surrounding the handling of the poll and then forward the case for judicial review.

Citing inconsistencies in the vote count, the controversial calculation of party-list seats and uncounted ballots from New Zealand, Mr Ruangkrai said the EC's handling of the poll may not be constitutional.

"There are doubts as to whether the EC has followed the rules and regulations. If its actions are in breach of the constitution, the outcome could be invalid. The ombudsman will be asked to consider this," he said.

Meanwhile, the debate over the calculation and allocation of the 150 party-list seats continues unabated with the EC insisting that at least 25 parties are eligible according to their share of the vote.

Somchai Srisutthiyakorn, a former Democrat Party MP candidate who previously served as an election commissioner, said on Monday the calculation must follow both Section 91 of the constitution and Section 128 of the organic law on the elections of MPs.

The Democrat member also said according to that process only 14 political parties were eligible for party-list seats.

Mr Somchai said he would submit his calculation to the EC this week and would ask the poll agency to read the relevant Section 128(5) carefully.

He insisted that the required number of votes for one seat is about 71,000, and any party with less does not qualify.

According to Mr Somchai, the EC should not make a decision until it has all the information. However, he said the issue is unlikely to render the election nullified because the result can be corrected.

He said it is not possible to ask the Constitutional Court to intervene until the EC announces the official result.

The EC deputy secretary-general, Sawaeng Boonmee, yesterday defended the handling of the election, saying the agency is being unfairly accused of not being transparent or fair. He said the poll agency had answers to every query and most of the allegations had been made by nameless people on social media to gain "other benefits".

"If there is evidence about unfairness or dishonesty, it should be submitted to the EC for examination. Those suspicions shouldn't be used to make accusations against the EC," he said.

According to Mr Sawaeng, the contest was expected to be fierce so every step from ballot printing to the vote count was designed to prevent rigging.

The March 24 poll was also extensively monitored by observers from various sectors including political parties and media outlets and the more than 12,000 candidates vying for House seats.

The number of complaints of fraud is much lower, in the hundreds, compared with previous polls which saw thousands of complaints, he said.

He also suggested that the way the party-list seats are distributed is complicated and totally different from previous elections.

Taweesak Suthakavatin a member of the National Legislative Assembly who took part in the scrutiny of the law on the elections of MPs, yesterday stood by the EC's calculation method, but took the agency to task for being too slow to explain the issue.

"There's only one formula. If someone is to blame, it's the EC for being slow to explain it. But the agency may want to wait for the final numbers in case there are reruns," he said.