The protest leader-turned-MPs who turned up at the parliament to register their MP status included Natthawut Saikua, Korkaew Pikulthong, Weng Tojirakarn, Wiphutalaeng Pattanaphumthai and Payab Pankate.
The core leaders of the United Front for Democracy against Dictatorship (UDD) earlier announced that they would not register their MP status as they wanted to wait for the endorsement of Mr Jatuporn Prompan, now detained at Bangkok Remand Prison on terrorism charges.
Mr Natthawut, however, said the Red Shirt leaders have to register their MP status today, as a House meeting will be held on Monday and they have been waiting for Mr Jatuporn's endorsement until the last minute.
Mr Natthawut said he believes the EC would finally endorse Mr Jatuporn as a party-list MP, but the Pheu Thai party will wait through the 30-day timeframe as required by the law for the EC decision.
If the poll agency does not endorse Mr Jatuporn, we would assign a legal team to file a lawsuit against the EC, as it has no authority to suspend the detained leader, according to the new MP.
Following remarks of EC commissioner Sodsri Satayatham that undue Red Shirt pressure could lead to possible violence and that the army might intervene to supervise the situation, Mr Natthawut reasserted that the Red Shirt had no plans to pressure the election agency and if the EC has been threatened, it's not actions endorsed by the Red Shirt movement.
Regarding the future of the UDD after the election, Mr Natthawut said the civil movement would continue, but that the protest leaders would discuss ways to adjust their approach.
Following reports that the Red Shirts will propose key leader Col Apiwan Viriyachai as new House Speaker, Mr Natthawut said any MP has right to support anyone for the top job, but in the end it depends on the consideration of the Pheu Thai party executives to decide.
Meanwhile, prime minister-to-be Yingluck Shinawatra on Sunday pledged to name the House Speaker by Monday, expressing confidence that the person who is selected will not be opposed by UDD leaders or party members.
In the latest development, Col Apiwan on Sunday announced his withdrawal from consideration as House Speaker, as well as other posts in legislative power, citing concerns for the image of the House of Representatives.
Col Apiwan reasoned that, while he has done his best when serving as deputy House Speaker, for a better image of the parliament and to assuage MPs in other parties who feel uneasy about the position, he would withdraw himself from consideration to pave the way for national reconciliation and create better atmosphere in and out of the Pheu Thai party.
"I reaffirm that no one in the party put pressure on me to withdraw. This is my own decision and has nothing to do with the Red Shirt movement," asserted Col Apiwan.
The Red Shirt leading figure added he has already informed his decision to incoming premier Yingluck Shinawatra and Pheu Thai party leader Yongyuth Vichaidit, while saying he is ready to take on any administrative post as assigned by the party without any preconditions.