The labour movement will get a new president on Thursday in a move to refresh its leadership.
The incumbent president of the National Trades Union Congress (NTUC), Ms Diana Chia, is not seeking re-election at its National Delegates Conference, which starts today.
The 59-year-old is NTUC's first woman president and was elected in 2011.
Her retirement, along with that of two other top grassroots unionists, was announced by Prime Minister Lee Hsien Loong at a dinner last night to mark the conference's opening.
Besides Ms Chia, NTUC vice-president Nora Kang, 60, and secretary for financial affairs Lim Kuang Beng, 59, are also not seeking re-election to NTUC's central committee, its highest decision-making body.
On her decision to step down, Ms Chia, who is a nurse, said: "As I cannot serve the full term, I should leave and let the new leadership take over."
In 2011, the NTUC implemented a self-imposed leadership renewal rule that requires top union leaders to voluntarily step aside for new blood when they turn 62.
If the trio were to stand in the elections and win, their age would prevent them from completing the full four-year term, which ends in 2019. Elections to the central committee are held every four years.
"They have been effective union leaders," said Mr Lee of the trio. "They understand workers' concerns, they know the national interest, they have influenced the Government and helped the Government to implement policies which benefit workers."
Mr Lee said he had worked closely with them. "We speak candidly with one another, we know how each other thinks, we can rely on each other to get things done."
Union sources said the front runners for the president post are two incumbent vice-presidents: Mr K. Karthikeyan, 56, and Mr Edwin Lye, 45.
Mr Karthikeyan is general secretary of the United Workers of Petroleum Industry and was a Nominated MP in the previous Parliament, while Mr Lye is general secretary of the Singapore Teachers' Union.
A total of 27 union leaders are vying for the 21 seats in the central committee. Among them are secretary-general Chan Chun Sing, who is facing his first union elections since joining the NTUC this year.
According to its Constitution, the 21 elected members have to elect among themselves the office bearers of the committee.
In his speech last night, Mr Lee urged the unionists to give a strong mandate to the team of leaders.
"At the national level, we just had our election and we have voted in a new Government," he said. "I am honoured that Singaporeans gave my team a strong mandate to take the country forward.
"Now, it is NTUC's turn to hold your elections. And you have to give your team a strong mandate to take the NTUC forward, " he said to applause from the audience.