Four deputy leaders of the Democrat Party on Wednesday resigned from their posts in order to step up efforts to stop the blanket amnesty bill proposed by the ruling Pheu Thai Party.
Their resignations are effective from 9am, although the four will continue in their roles as MPs.
They are former finance minister Korn Chatikavanij, Thaworn Senneam, Issara Somchai and Siriwan Prasjaksattru.
Mr Issara said his resignation would make it easier for him to lead people to rally against the revised amnesty bill, which aims to "whitewash" fugitive former prime minister Thaksin Shinawatra.
The Democrats will hold a mass rally against the bill on Thursday at Samsen railway station in Bangkok’s Dusit district at 6pm, he said, corresponding with the House of Representatives' consideration of the legislation.
He said he expected more than ten thousand of people would join the protest and suggested the number of people protesting would surge even higher over the weekend.
A permanent rally stage will be set up at the railway station, which is not far from the parliament building compound, and the rally will go on until the controversial bill is withdrawn from parliament, he said.
The four Democrats have resigned as deputy party leaders but will maintain their status as MPs so that they have immunity during the planned rally, in the event that police issue warrants for their arrest.
A meeting of Pheu Thai Party MPs on Tuesday passed a resolution to vote in support of the blanket amnesty bill in its second reading on Thursday.
The resolution prohibits the party’s MPs, particularly those who are members of the red-shirt United front for Democracy against Dictatorship (UDD), to vote against the bill.
Pheu Thai Party leader and Interior Minister Charupong Ruangsuwan said party MPs must support the bill and insisted it would not be withdrawn, despite strong opposition from several groups.
He argued that the consideration of an amnesty bill has been delayed for more than two years, adding that Pheu Thai will be accused of failing to comply with its election promises if it does not push the legislation.
Party secretary general Phumtham Vejjayachai said all Pheu Thai MPs must attend the parliamentary meeting and vote in support of the amnesty bill on Thursday.
Mr Phumtham said coalition partners of the Pheu Thai-led government had also agreed to vote in support of the bill.
But Pheu Thai list MP and co-leader of the UDD Weng Tochirakarn said he disagrees with the bill's proposal to grant amnesty to those who ordered the crackdown on red-shirt protesters in May 2010, so will abstain from voting on the bill.
Another UDD co-leader and Deputy Commerce Minister Natthawut Saikua said on Tuesday that red-shirt groups strongly oppose the bill granting amnesty to former prime minister Abhisit Vejjajiva and his former deputy for security affairs Suthep Thuagsuban.
Prime Minister Yingluck Shinawatra admitted she is concerned about the situation and called on groups opposing the amnesty bill to stage peaceful and lawful rallies and avoid blocking roads.