The Government will be revoking the work pass of a Malaysian who was arrested for participating in the May 8 and 11 illegal protests at Merlion Park.
Another two have had their visit passes cancelled, while 18 others will have their work passes reviewed after investigations are done, the Singapore police said in a statement on Tuesday night.
The 21 Malaysians were arrested on Saturday at a protest against the outcome of the recent Malaysian general election, despite an earlier police warning not to do so. The police have since issued conditional warnings to all 21 and their employers will be informed.
The eight men and 13 women are between 21 and 40 years old and are currently out on bail, the police said earlier. There was no information about their occupation or if any of them were students.
The latest action came after the police warned nine people for taking part in the first illegal gathering last Wednesday.
In the statement, the police said: "Foreigners living or working in Singapore must abide by Singapore laws, and should not import the issues or politics of their countries of origin to Singapore."