Police are investigating local activist Gilbert Goh for carrying out a public assembly without a permit.
Last Saturday, Mr Goh posted a picture on his Facebook page showing him holding up a placard outside the Immigration and Checkpoints Authority (ICA) building.
The placard had the words "Please ban all flights from India we are not racist! Just being cautious".
The post had more than 400 comments and had been shared more than 1,400 times as at yesterday morning.
A police spokesman said they received a report on May 1 alleging that Mr Goh had taken part in a public assembly without a permit.
"Mr Gilbert Goh did not have a police permit to carry out the public assembly," said the spokesman.
"The police would like to remind the public that organising or participating in a public assembly without a police permit in Singapore is illegal and constitutes an offence under the Public Order Act."
The authorities are investigating.
All long-term pass holders and short-term visitors who have travelled to India within the last 14 days have been barred from entering or transiting through Singapore since April 23.
The move was announced by the multi-ministry task force on Covid-19, following a surge in cases in India.
India's daily death toll from Covid-19 hit a record 3,689 deaths on Sunday, taking the country's death toll to more than 215,000.
It also reported more than 400,000 new cases last Saturday, taking its total caseload to more than 19.1 million.