Party deputy secretary-general Thaworn Senniam said the Election Commission had exceeded its mandate in calling another round of voting in the 38 constituencies that failed to give the sole candidate the minimum requirement of at least 20 per cent of eligible votes in the April 2 general election.

Thaworn claimed that the EC had erred in accepting additional candidatures for the repeat vote, seen as a ploy to help Thai Rak Thai candidates overcome the 20-per-cent rule.

"The EC appears to be going out of its way in order to favour one political party," he said, citing provisions of the electoral laws that he claimed the EC had violated.

The EC was required to allot five days for candidates to register, but it set aside only two days for additional candidates to register for the by-election, he said.

Furthermore, the EC was obliged to finish registering candidates within 20 days of the Royal Decree for the snap election, he said. This deadline had expired because the decree was enacted in February.

The court is expected to rule next week on whether the case merits judicial review.

EC secretary-general Ekachai Warunprapha said yesterday that the agency had strictly followed the electoral law in a bid to complete its task of filling all 500 seats in the House of Representatives.

He rejected an accusation that the election commissioners were biased in favour of "a large political party" in its alleged attempt to avoid the 20-per-cent rule.

"We are not helping any party in particular. The decision to open new candidate registration was agreed by all the election commissioners. Don't you sympathise with the EC? We have to announce the [official] election result within 30 days after the voting day," he said.