Democrat MP Panich Vikitsreth has defied a request to stay away from parliament by taking his seat to vote on amendments to the constitution.
House speaker Chai Chidchob asked Mr Vanich yesterday to take a leave of absence to prevent possible legislative problems over his status as an MP, which remains unclear after his conviction last week by a Cambodian court.
Mr Chai met with parliamentarians to discuss Mr Panich's status before the joint meeting of the houses began debating the amendments. He then told the Democrat MP he wanted him to absent himself from the session.
Mr Panich and four other Thais were given nine-month suspended jail sentences last Thursday by a Phnom Penh court for illegal entry into Cambodia.
The MP yesterday stood firm on his right to attend the joint meeting. He insisted he was still a member of the lower house and so was entitled to cast his vote.
The Democrat MP voted in support of the charter amendments.
The Election Commission has decided to set up a subcommittee to investigate Mr Panich's conviction and recommend whether he should lose his seat.
Commissioner Prapan Naigowit said the EC received a report yesterday from the Foreign Affairs Ministry concerning the court verdict against Mr Panich.
The law bars those convicted of a crime from sitting in the lower house. The subcommittee must decide if a conviction in a foreign court would disqualify Mr Panich of his MP status.
The EC will forward its decision to the house speaker. If it finds Mr Panich should be stripped of his seat, the speaker would forward the matter to the Constitution Court for a final ruling.
Section 106 (5) of the constitution states that an MP will lose their seat if sentenced to jail, regardless of whether the sentence is suspended, except where the offence is considered unintentional.