The Government cracked down on left-wing trade unions and old boys' associations of Chinese schools in November 1965 to prevent the escalation of protests linked to the then Nanyang University.
In a nine-hour operation that began in the early hours of Nov 14, the Special Branch raided the offices of left-wing unions that were organising mass support for student agitators of the university.
The operation took place amid a three-week boycott of classes at the university in protest against the recommendations of a committee headed by Professor Wang Gungwu. The committee had proposed measures such as the opening up the university to students of all streams, which sparked fears that the university's Chinese character would be diluted.
The Straits Times reported that in the operation against the left-wing unions, the premises of eight union and four alumni associations were raided and at least 12 people were arrested or detained for interrogation.
Documents and pamphlets related to the agitation at Nanyang University were seized during the operation. The Singapore Commercial Houses and Factory Employees' Union in Wayang Street was the first to be raided.
Its president Chen Sin was picked up from his home and interrogated by Special Branch officers.
Other unions that were raided included the Singapore Tailors' Union in Waterloo Street.
The opposition Barisan Sosialis criticised the crackdown and demanded the unconditional release of all the people arrested.
Then Prime Minister Lee Kuan Yew, speaking at an anniversary event of Nee Soon Community Centre, issued a warning to Chinese-language agitators.
"Whoever tries to use language, religion or communal sentiments will be smacked down before they can create mischief," he said.
A few days later, the Government dissolved 11 old boys' associations of Chinese schools that had actively supported student disturbances linked to the dismissal of 85 student agitators at Nanyang University. In the same week, the Government tried to allay the fears of those worried about the dilution of the university's Chinese character by affirming that it "will always be the Chinese university of independent Singapore, using Chinese as the medium of instruction".
The assurance was given after a meeting between government leaders headed by Labour Minister Jek Yeun Thong and representatives from the university, held after weeks of student agitation.
The police were called in to maintain order for classes to resume at the university at the end of November 1965.