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The 1966 by-elections were held over eleven months from 18 January through 2 November for seven constituencies. All of the vacancies were related to Barisan Sosialis resignations, which continued into the following year, with the sole exception being Joo Chiat's MP Fong Kim Heng. This was the first election of any kind in post-independence Singapore.
Background
On 8 December 1965, about four months into independence, the Barisan Sosialis began to boycott Parliament in response to the current legislature and its democracy as "phony". The first MP to resign was Lim Huan Boon on 31 December 1965, after which by-election nominations were called for Bukit Merah on 8 January. On nomination day, two more MPs, Chio Cheng Thun and Kow Kee Seng, resigned, followed by S. Thendayatha Bani the day after. A further two seats became vacant nine months later on 7 October, with the resignations of Chia Thye Poh and Lee Tee Tong. Two months later on 5 December, five of the remaining seven Barisan MPs, including Loh Miaw Gong also resigned. Another MP, Fong Kim Heng, resigned on 18 October, but Fong was from the PAP unlike the other 11, and cited health reasons.
Chua Chu Kang, Crawford and Paya Lebar constituencies were at stake in the second by-election, with nominations occurring on 1 March. The third by-election were for Bukit Timah, Joo Chiat and Jurong constituencies, with nominations occurring on 2 November. However, these elections went uncontested.
The aftermath of the boycott of the Parliament sparked mass arrests under the Internal Security Act (ISA), including that of Chia Thye Poh, who was detained under this act for 22 years without any trial, becoming the world's second-longest incarcerated political prisoner. Oppositions reached a low point, and Barisan Sosialis would begin to fell apart in the succeeding years.
The People's Action Party government would win every parliamentary seats in ensuing elections for the next 15 years, and to date still remained in power, winning at least two-thirds of all Parliamentary seats. The government would not witness opposition presence again until the 1981 Anson by-election.