Candidates and central executive committee members of political parties are barred from going on stage or speaking at election rallies other than their own.
Another rule the police set is that speakers at rallies, which will begin next Wednesday, cannot hide their faces. This is to ensure they can be held accountable for what they say.
"There shall be no sharing of rallies nor rally sites amongst different contesting political parties or independent candidates," said the Elections Department (ELD) in an advisory released on Tuesday.
These were among the new conditions set by the police for political parties contesting the Sept 11 General Election.
As many as 10 political parties - nine of which are from the opposition - and at least one independent candidate are expected to contest the coming polls.
Election rallies will be held over eight days, ending Sept 9, the eve of Cooling-off Day, before voters head to the polls on Sept 11.
The Straits Times understands that the rule was prompted by public safety concerns. Having supporters from different camps at rally sites runs the risk of overcrowding and possibly violence breaking out.
This rule does not apply to ordinary members of political parties, or to individuals without political affiliations who are not contesting the election as independents.
Political watchers say restricting candidates and party leaders from speaking at each other's rallies will likely affect the opposition more.
In the past, there were instances where opposition party members would speak at each other's rallies as a show of support and solidarity against the ruling party, said law professor Eugene Tan.
"If not for the rule, we will see smaller parties inviting speakers of other parties, and in a way there are concerns as to whether there may be people with an inordinate amount of air time," added the former Nominated MP.
Political analyst Derek da Cunha said the rule will affect the Democratic Progressive Party (DPP) if it continues to contest Bishan-Toa Payoh GRC under the banner of the Singapore People's Party (SPP).
DPP chief Benjamin Pwee declined to comment yesterday, while the SPP could not be reached.
People's Power Party secretary- general Goh Meng Seng said last night that he will challenge the new rule but declined to elaborate on how he plans to do so.
And while Singapore Democratic Party chief Chee Soon Juan has no plans to speak at the rallies of other parties, he said the ban "does not make sense".
He added that it was natural that different opposition parties may want to appear at their comrades' rallies to show support.
The ELD yesterday also asked contesting candidates to refrain from "negative campaigning practices" based on hate and denigration of their opponents.
They should also not make libelous statements, or say anything that may "cause racial or religious tensions or affect social cohesion".
Such behaviour, the ELD said, would be in breach of the law.
These rules, however, may just blunt the opposition's campaign on hot button issues such as immigration, said Dr da Cunha.
"Minor parties will simply have to curb their rhetoric on the immigration issue, for instance," he said.
Prof Tan disagrees, saying he does not expect it to stop opposition parties from criticising government policies so long as they do not denigrate anyone in aspects of race, language or religion.
Mr Tan Jee Say of the Singaporeans First Party said he was not overly concerned as he has "always behaved in a decent way, attacking policies rather than people".
The ELD also reminded candidates that films they plan to distribute or publicly exhibit must be submitted to the Media Development Authority for classification.
A ban on party political films still applies, while the use of aerial drones at nomination and assembly centres, rallies and other meetings is also not allowed.
• Additional reporting by Lim Yan Liang, Pearl Lee and Danson Cheong