Former Democrat leader Chuan Leekpai on Monday called for a clear explanation from the party of its position regarding the sexual harassment charges against former deputy leader Prinn Panitchpakdi.
Mr Chuan said he would not interfere in the work of the party executive, but asked them to show responsibility and clearly explain the party's position to the public. It was affecting the party's reputation and its supporters.
Democrat leader Jurin Laksanawisit and other leading members have said the allegations against Mr Prinn were a matter for the police to handle. The party would not protect or tolerate tolerate sexual harassment.
However, some party members have said this is not enough, because its executive members had chosen and appointed Mr Prinn a deputy leader.
Party-list MP Pimrapee Phanwichatikul posted a Facebook message on Sunday apologising to the public and party supporters.
"As an organisation in which the person accused of wrongdoing worked, we have to show responsibility," said Ms Pimrapee, who is on the party executive, without mentioning Mr Prinn by name.
Her strong message was also seen on the party's Facebook account.
Police have pressed charges in three cases against Mr Prinn - two for indecent assault and the other for alleged rape. He denied all allegations and was released on bail.
The rape accusation was registered with police by Hathairat Thanakitamnuay, wife of anti-government activist Thanat, better known as Luk Nut, at Lumpini police station on Thursday.
Her decision to bring charges came after an 18-year-old student filed a sexual harassment complaint against Mr Prinn at the same police station on Tuesday.
Mr Prinn, who is not an MP, resigned from all positions in the Democrat Party on Thursday to fight the allegations.
His father Supachai Panitchpakdi was deputy prime minister in charge of economic policy when Mr Chuan was prime minister.