The National Solidarity Party's (NSP) secretary-general Lim Tean has quit the party, less than two years after he took up the post.
Announcing his resignation in a Facebook post yesterday, Mr Lim, 52, cited a "fundamentally different" approach to politics from the party for the split.
He said the turning point came after he gave a speech in March at an event about the impending 30 per cent water price hike.
"It was an issue that troubled most Singaporeans and one that I thought the NSP would wholeheartedly embrace," the legal consultant wrote.
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"I was therefore surprised to learn that elements in the party disapproved of me taking part in the event."
Mr Lim also said he had "great differences" with the party over changes to the elected presidency - pointing out that the NSP chose to remain silent on the issue.
Parliament approved changes to the elected presidency scheme last November, which included a provision for a reserved election for candidates from a particular racial group if there has not been a president from that group after five consecutive terms.
"I eschew the type of politics where people, especially politicians, are frightened to speak up because of personal considerations. To me, that is a complete dereliction of one's duty," said Mr Lim.
In the same post, he also said he informed NSP president Sebastian Teo of his resignation on May 18.
In most political parties, the secretary-general is the party's leader, but the NSP is led by its president. Its secretary-general is widely regarded to be the party's No. 2.
When contacted, Mr Teo said Mr Lim's disagreements with the party had more to do with procedures than opinions.
He pointed to party protocol that requires council members to seek approval from the entire 15-member council before commenting publicly on issues - a rule that Mr Lim was frustrated with.
"It's good and bad - we might be slow to process and issue comments, but the good thing is when we do so, everyone agrees on it and can be responsible for it," said Mr Teo, adding that the NSP was a party "developed on consensus".
"This is an organisation and these are the procedures we have. If people don't follow the rules, how do we manage the party?"
In a phone interview, Mr Lim told The Straits Times that he respects Mr Teo and is parting on good terms with him.
Asked about the party's unhappiness with his speech on the water price hike, he replied that nothing he said was "out of line".
"That's my position, I don't want to go beyond that," he added.
He intends to make an announcement on his future plans over the next few days.
Mr Lim was appointed as the NSP's acting secretary-general on Aug 30, 2015, just before the 2015 General Election.
He was part of a five-man NSP team that contested Tampines GRC - where the NSP garnered 27.9 per cent of the vote against the incumbent People's Action Party.
Mr Lim is the fifth secretary- general to leave the party since the 2011 General Election - others who have held the post include Ms Hazel Poa, Mr Goh Meng Seng, Mrs Jeannette Chong-Aruldoss and Mr Tan Lam Siong.