Senate Speaker Pornpetch Wichitcholchai insisted on Wednesday the House of Representatives has no authority to probe the qualifications of senators.
His comment is a response to a report that the opposition plans to submit an urgent motion seeking a probe into the controversial Senate selection process.
Mr Pornpetch, who was named a member of the Senate selection committee but later resigned, said MPs who want to examine the senators' qualifications would have to find other channels because the House is not empowered to do so.
He said the House Speaker, Chuan Leekpai would have to decide if the motion would be accepted.
Pheu Thai MP Suthin Khlangsaeng said the opposition's motion would ask the House of Representatives to set up a committee to investigate four questions related to the Senate selection process.
These four are whether a selection panel was actually set up to search for potential candidates to fill 194 seats; if there were criteria or regulations for the selection; if the appointments of those with close ties to the regime is a breach of the charter or a conflict of interest; and if a budget of 1.3 billion allocated to fund the Senate selection was properly disbursed.
Mr Chuan said he would examine the opposition's motion and decide whether it is within the House of Representatives' jurisdiction to proceed.
Even if it is within the House's jurisdiction, Mr Chuan said the issue will be forwarded the government MPs to decide if a joint committee should be set up to deliberate the issue.
Meanwhile, Ruangkrai Leekitwattana, a former member of the dissolved Thai Raksa Chart Party, on Wednesday lodged a petition with the Office of Attorney-General (OAG) asking it to seek a Constitutional Court ruling on the Senate selection process.
He asked if the Senate selection process itself could be unconstitutional because the appointment of the selection committee chaired by Deputy Prime Minister Prawit Wongsuwon was not published in Royal Gazette.
According to Mr Ruangkrai, the petition also asked the court to revoke the status of 194 senators.
If the court goes ahead, the status of Prime Minister Prayut Chan-o-cha who was selected by them will be nullified accordingly, he said. If the OAG does not forward the case to the court within 15 days, Mr Ruangkrai said he will lodge the petition himself.