The Setthakij Thai Party led by Thamanat Prompow has vowed to vote against Prime Minister Prayut Chan-o-cha and cabinet ministers targeted in the upcoming no-confidence debate, in what is seen as a bid to force a change of government leadership, a party source says.
The party wants to demonstrate its clear stance against the government after sitting on the fence and refusing to commit itself to either the coalition or the opposition.
The move follows its candidate's defeat in the by-election in Lampang's Constituency 4 on Sunday as a rival from the Seri Ruam Thai Party, which is in the opposition camp, secured victory.
Deputy Setthakij Thai leader, Wichit Plangsrisakul, said on Tuesday the defeat in the by-election showed that people disagreed with the party supporting the government.
In light of this, its strategic committee decided that list-MP Boonsing Warinrak and Pai Leeke, an MP for Kamphaeng Phet, should quit their roles as government whips.
The two MPs on Tuesday submitted a letter informing the prime minister they want to resign from those roles with immediate effect.
A party source said people have been confused by the party's stance. As such, it wants to drive home the message that it will turn its back on the government and will vote against the PM and the targeted ministers in the no-confidence motion, the source said.
Mr Boonsing, who also serves as the party's registrar, admitted the by-election defeat was unexpected as the party was previously confident it would secure a win. The party needs to identify and fix problems, he said.
"The party previously announced it would work in the best interests of the public and oppose anything that is not right. We agreed with the government on certain issues, but we also opposed it on some others.
"The party's unclear position may be to blame for its defeat in the poll," Mr Boonsing said.
Pichet Sathirachawal, a list-MP for the ruling Palang Pracharath Party (PPRP) and leader of the so-called "Group of 16" comprising MPs of micro-parties and some PPRP members, described Setthakij Thai's by-election defeat as an upset.
"If the party's leader ... wants to continue to engage in politics, he must declare a clear stance against the government," Mr Pichet said.
Setthakij Thai is home to 18 MPs, including Capt Thamanat, who were all expelled by the PPRP for acting as renegades.
Yet Capt Thamanat remains steadfast in his loyalty to Deputy Prime Minister and PPRP leader Prawit Wongsuwon, even though he was accused of being the mastermind of last year's censure debate revolt against Gen Prayut.
At the time, Capt Thamanat served as the PPRP's secretary-general and was seen as Gen Prawit's right-hand man.
Setthakij Thai is seen as a key player in the no-confidence vote as Capt Thamanat has made it clear he will not support Gen Prayut, but he will vote for Gen Prawit.
Gen Prayut is expected to be the main target for censure while Deputy Prime Minister and Commerce Minister Jurin Laksanawisit is also expected to face fierce grilling over the high prices of consumer goods caused by rising fuel prices.
Energy Minister Supattanapong Punmeechaow is not among the censure targets.
Pheu Thai Party leader Cholnan Srikaew previously said he expected the debate to last five days, probably from July 18-22.
It will be the last censure debate the opposition can initiate before the government's tenure expires next March.
In other news, Deputy Prime Minister Wissanu Krea-ngam said on Tuesday a ruling by the Constitutional Court will end any controversy surrounding a method using 500 to calculate party-list seats.
"If the issue goes to court, let's wait for a ruling which will clarify everything," he said.
Last Wednesday, a majority of MPs and senators voted in favour of the calculation method, seen to benefit small parties at the expense of big ones, particularly Pheu Thai.