Oppositions MPs have slammed the Senate for announcing it planned to shoot down charter amendment proposals submitted by the opposition bloc and three government coalition parties.
The bills would cut its powers in the selection of a prime minister, while the Palang Pracharath Party bill which the Senate says it will support keeps them in place.
Chief opposition whip and Pheu Thai MP Sutin Klungsang said the Senate owed the public an explanation about why it would vote for the PPRP-sponsored draft but reject the others. He said the proposals put forward by the opposition and the three coalition parties were almost identical to the PPRP's.
"Since these drafts are almost identical, why would the senators accept only the PPRP's charter amendment proposal?" he asked. "You don't adhere to principles, do you."
The opposition camp and three coalition parties -- Bhumjaithai, Democrat and Chartthaipattana -- submitted a total of 14 charter amendment motions on Wednesday to revamp multiple sections of the constitution. While those drafts aim to deal with many key areas in the charter, they all seek to curb the Senate's power in the selection of a prime minister.
However, the PPRP-sponsored draft, which will be debated in a joint sitting of MPs and senators next week, left the issue of the PM's election process untouched and is expected to sail through. What the drafts had in common was a proposed amendment to the election system to restore the two-ballot method.
Senator Kittisak Rattanawaraha had said on Wednesday that most senators had agreed to only approve the PPRP's draft and reject all others if it made drastic changes to the constitution. According to Mr Sutin, one of the other drafts sought to rewrite Section 256, which would involve replacing the current charter.
He said that in the previous charter amendment process, a bid to amend Section 256 had been endorsed in the first reading but failed to clear parliament because the Constitutional Court ruled a national referendum was required.
Senator Somchai Sawaengkarn on Thursday argued the upper house had been given the power to join MPs in selecting a prime minister by a national referendum. Also, the Senate was not authorised to nominate a prime minister, only to vote on the issue, and Senators only serve five-year terms.
Chinnaworn Bunyakiat, deputy chief government whip and Democrat Party MP, said the 14 charter amendment proposals would likely be included in a parliamentary session on June 23-24. The opposition, government and Senate would be allocated six hours each for the and a vote was expected to take place on the afternoon of June 24.