The police have issued conditional warnings to nine people for "actively participating in the illegal gathering" at the Merlion Park on Wednesday.
In a statement released on Friday evening, the police also said their work and visit passes are being reviewed by the authorities.
"Their employers will be informed of this. Further investigations are ongoing," the statement added.
A crowd of Malaysians had gathered near the landmark at about 9.30pm on Wednesday to protest against what they claimed were rigged elections in their country. Dressed mostly in black, the crowd of mainly young people stood at Merlion Park in Marina Bay, holding up signs and chanting occasionally.