Red shirts have threatened to hold a mass rally if it believes the Constitution Court's ruling on the validity of the Pheu Thai-backed draft charter amendment is unfair to the ruling party.
"We will hold a mass gathering if the court fails to uphold justice and if the verdict adversely affects the Pheu Thai Party," and list MP and red shirt co-leader Korkaew Pikulthong told about 500 red shirts gathered at Lan Khon Muang in Bangkok yesterday.
Pheu Thai wants to amend Section 291 of the charter to pave the way for the establishment of a constitution drafting assembly.
Five petitions were lodged with the Constitution Court in May, asking the court to intervene in the charter change process under way in parliament.
Those lodging the petitions claimed that a section of the bill authorising the writing of a whole new charter was tantamount to overthrowing the constitutional monarchy and acquiring administrative power unconstitutionally.
The court is scheduled to hear witnesses from the plaintiffs and Pheu Thai on Thursday and Friday. A verdict is expected right after the hearing finishes.
Mr Korkaew said he would initiate a campaign for one million signatures to call for the impeachment of the charter court judges.
Chaturon Chaisaeng, a former Thai Rak Thai executive who recently completed a five-year political ban, said there was a high chance that Pheu Thai would lose the case.
"If I'm right, it's time for us to come out and fight," Mr Chaturon told the crowd.
Constitution Court judge Jarun Pukditanakul yesterday said the court would stick to the facts in its ruling.
The ruling would be handed down regardless of comments or pressure from either supporters or opponents of the charter rewrite, he said.
Every judge would stand firm on legal principles and would not be influenced by outside factors, he said.
Among the 16 plaintiff witnesses will be Thammasat University rector Somkid Lertpaitoon, former prime minister Anand Panyarachun and Abhisit Vejjajiva, the opposition leader.
The four defendant witnesses will be Yongyuth Wichaidit, a deputy prime minister and the leader of Pheu Thai; Jarupong Ruangsuwan, the transport minister and Pheu Thai secretary-general; Pokin Polakul, a Pheu Thai member; and Pitoon Poomhiral, House secretary-general.
Meanwhile, Pheu Thai announced yesterday that former deputy transport minister Phumtham Wetchayachai would succeed Plodprasop Suraswadi as party director.
Mr Plodprasop, who is also deputy Pheu Thai leader and the science and technology minister, has resigned as director due to work overload.