A group of Pheu Thai supporters is calling for the party to break away from the Move Forward Party (MFP) over an internal rift regarding the House speaker post.
The group, however, still supports Pheu Thai's promise to vote for MFP leader Pita Limjaroenrat as the next prime minister and allow the MFP to lead the formation of a new coalition, said Niyom Nopparat, a leader of the group.
It also calls on Pheu Thai to support the MFP-led attempt to rewrite the constitution for the people, he said.
Several group members gathered outside the headquarters of Pheu Thai in Bangkok on Sunday and submitted an open letter containing these calls to the party.
If the MFP fails to gather enough MPs to form a new coalition government, the group believes Pheu Thai, which won the second-highest number of House seats after the MFP, should have the right to lead the formation of a new coalition, Mr Niyom said.
The group aims to make the MFP realise that it will be difficult to form a government without Pheu Thai by its side, he said. "We wish the MFP success in its attempt to form a coalition and urge Pheu Thai to support the MFP and all other coalition parties by voting for Mr Pita to become the prime minister," he said.
He insisted the group's motive wasn't a political game or an attempt to generate more conflict between Pheu Thai and MFP.
An internal conflict in the group of eight parties that agreed to form a government together stems from attempts by a group of people who spread distorted information against Pheu Thai, he said.
Anusorn Iamsa-ard, a key figure who serves as deputy secretary-general of Pheu Thai's committee on political strategies, received the open letter from the group and promised to relay the calls to the party's executives for consideration.
"In a democracy, differences of opinions are perfectly fine as long as they are constructive and straightforward, not ones that distort to devalue or accuse someone like us, Pheu Thai," Mr Anusorn said.
Meanwhile, whistleblower Chuvit Kamolvisit posted on his Facebook page about what he described as "a new secret deal without the MFP".
According to Mr Chuvit, secret negotiations have been conducted to make the MFP an opposition party when it fails to gather more than half of the House seats required to form a government.
Pheu Thai, Bhumjaithai Party, Palang Pracharath Party, Democrat Party and Charthaipattana Party will then form a coalition instead under a secret deal called "come home", a reference to the former prime minister Thaksin Shinawatra who is waiting in Singapore, he said.
Mr Chuvit refused to name those engaged in the alleged negotiations. "I think I smell something rotten, like fake democracy," he said.
Pheu Thai leader Cholnan Srikaew said the party will consider the group's calls, especially their suggestion for Pheu Thai to leave the MFP-led alliance.
In this situation, to have a democratic government is more important than anything else, he said, adding while differences in opinions among parties attempting to form a government could still be reconciled to achieve the ultimate goal.
"Pheu Thai does listen to opinions from all sides, especially those who support the party," he said.
He denied rumours that Pheu Thai was offered the energy minister position in exchange for the House speaker post, saying the party has yet to begin formal discussions on the allocation of cabinet portfolios.
A meeting of the coalition parties has been called for tomorrow to deal mainly with the cabinet minister quota each coalition party will be entitled to receive, said a source.
MFP secretary-general Chaithawat Tulathon said he believed there would be enough time left after tomorrow's meeting for informal talks with the coalition parties on the House speaker post.
Meanwhile, the Election Commission (EC) will today start a probe into whether Mr Pita was eligible to run in the election, due to his ownership of shares in a media company.