The organiser of a Labour Day protest who had planned to put up a poster of the Prime Minister at Hong Lim Park for Singaporeans to deface has been warned against doing so.

The police, in a statement on Wednesday, said it had advised Mr Gilbert Goh that the actions may constitute offences under the Penal Code and the Miscellaneous Offences (Public Order and Nuisance) Act.

"The Speakers' Corner is a designated outdoor area for Singaporeans to express their views in public," a police spokesman said.

"Mr Goh is free to hold his planned demonstration at the Speakers' Corner, but it is also his responsibility to ensure that any activities conducted during the demonstration do not contravene the law."

He has also been asked to remove online posts which encourage protestors to "conduct activities that might be against the law," said the police.

Mr Goh, who is planning a protest on Thursday to speak out against the hiring of foreign workers, said in a Facebook post on Wednesday that he had received a call from a police inspector.

The 52-year-old added: "But that doesn't mean we can't scold him (PM Lee) for his errant pro-foreigner policies right?"

On April 19, he had put up a Facebook post criticising the Government's foreign worker policies.

He said that he would put up a "huge poster" of the Prime Minister during the May 1 event for protestors to "vent their anger".

He suggested that they could spit, throw eggs, splash dog excrement, draw graffiti and kick it.