SINGAPORE - A party member who helped draw up some of the Singapore Democratic Party's (SDP) policies has left the party, citing irreconcilable differences with party boss Chee Soon Juan.

Mr Jeremy Chen, a PhD student at the National University of Singapore Business School, said in his resignation letter to the party that he was unhappy with certain actions taken by Dr Chee. He posted the letter dated Tuesday on his blog the same day.

One such action was his removal from the mailing list of the SDP's organising division, an internal group for party members, the 32-year-old said in his letter.

He also wrote it was not clear to him why it was done, although he said Dr Chee had told him that his social media activity was the reason for his removal from the list.

"Before I even left the party, communication from me to the party mailing list was swiftly cut off soon after I replied to someone who wrote to the mailing list about 'a (party) member'" (me) criticising CSJ (Dr Chee) and asking, 'What is being done about this?'," wrote Mr Chen.

"That was extremely annoying (and) an act seemingly directed at preventing party members from knowing more about misconduct by a party leader."

Mr Chen also refuted Dr Chee's recent comments to the media that SDP has a "good slate" of new candidates for the coming general election.

"Who are the new people coming in? Because in all seriousness, I really don't know," he said. "Even people who are currently close to the action can't name these "new people" who might be candidates."

In an online response on Wednesday, SDP assistant secretary-general Christopher Ang said the party had repeatedly cautioned Mr Chen against making offensive posts on Facebook, but to no avail.

Mr Ang cited disparaging posts Mr Chen had made about both People's Action Party and opposition politicians, including former Prime Minister Lee Kuan Yew and Workers' Party chairman Sylvia Lim.

"The party then conveyed to Jeremy that if he continued with such Facebook posts, he cannot play a prominent role in the party," said Mr Ang. "This is the only point of contention the party has with him."

Mr Chen had helped launch some of SDP's policy proposals, including a public housing policy paper and an alternative population 'White Paper'. He also detailed in his blog his work on a Central Provident Fund position paper and an election strategy brief for the party.