Police are investigating six Malaysians under the Public Order Act for holding a public assembly without permit.
The four men and two women were approached by police at Tampines Central on Sunday afternoon at about 4pm while holding placards and posters that urged Malaysians residing in Singapore to return home to vote in the May 5 general elections.
The six had, earlier that day, been part of a bigger group of about a dozen Malaysians who had raised their placards at various spots in the Bugis area, including outside Albert Complex and the Queen Street Bus Terminal, and later at Bedok.
The signs, in a mix of Mandarin, English and Malay, read "Please go back to vote" and "Tomorrow will be better", among other slogans.
In a statement responding to media queries. police said a permit is required to hold any public assembly or to conduct any public procession.
"Police would like to remind the public that conducting such activities without a Police permit is illegal in Singapore," said the statement.
"Foreigners should also refrain from importing their domestic political activities into Singapore."
No charges have yet been filed.