A fierce debate is expected in parliament on Tuesday as MPs and senators hold a joint session to examine proposed amendments to two organic laws aiming to accommodate a dual-ballot election system following second and third readings.
The bills, which have been vetted by the House-Senate committee, deal with political parties and the elections of MPs, and its contents divide lawmakers.
One key issue is the calculation method for party-list votes.
The majority of the scrutiny committee has opted for the use of 100 to calculate the number of party-list votes gained by all parties nationwide as proposed by major parties. Meanwhile, small parties argue for the use of 500 to calculate party-list seats, with 11 minority committee members asking to address the chamber on this point.
The number 100 comes from the total party-list MPs while 500 refers to all the constituency and party-list MPs. Under the amended constitution, there would be 400 MPs from constituencies throughout the country, up from the current 350, and 100 party-list MPs, down from 150, in the next poll.
Somkid Chueaknong, Pheu Thai MP for Ubon Ratchathani, said on Monday that the calculation method has been finalised but there are "attempts to confuse the public".
All of the drafts that were adopted in the first reading proposed the use of 100 in the calculation, he insisted.
"Small parties have to work hard to strengthen themselves they should consider merging with larger parties if they believe the formula will benefit large parties at their expense," he said.
Chinnaworn Boonyakiat, Democrat MP for Nakhon Si Thammarat, said government whips will stand by the committee's decision.
Nirote Sunthornlekha, Palang Pracharath Party MP, said on Monday that the ruling party has no preference over the matter, and it is up to lawmakers to decide on how to calculate party-list votes.
Eighteen small parties on Monday asked Chatchawal Kong-udom, the Thai Local Power Party leader, to represent them in the planned debate on the amendments.
Mr Chatchawal said he agreed with the use of 500 to calculate party-list seats while Kowit Puangngam, a list MP for TLPP, noted the party might break ranks from the coalition government in a vote.