Council chairperson Jamal Md Yunus said the organisers of Janji Bersih were playing politics and trying to cause hardship for petty traders and the public.
"This time, we will take aggressive action to prevent this from happening and they will not be able to anticipate what we will do.
"We have 98,000 members and we will discuss plans during a Aidilfitri meeting. They (Janji Bersih) are trying to soil the auspicious Merdeka Day celebration," he told Berita Harian.
Jamal (right) urged Janji Bersih organisers, in particular national laureate A Samad Said, to reconsider their plan in order to "avoid a battlefield" scenario.
Contacted on this threat by Malaysiakini, Samad declined comment.
Last Thursday, 26 NGOs announced plans to hold the Janji Bersih gathering at a corner of Dataran Merdeka, where the federal government sponsored countdown event will take place.
The organisers have urged supporters to show up in yellow to symbolise their cause.
Unlike previous Bersih activities, the police and federal government have been mostly nonchalant about Janji Bersih,.
Jamal and the KL Petty Traders Action Council are among the first to voice strong opposition.
Previously, Jamal and his group claimed that the Bersih 3.0 rally on April 28 had caused a massive loss of income for Kuala Lumpur petty traders and are suing Bersih leaders for damages.
Jamal, a luxury car dealer and restauranteur, also offered a Lamborghini and a BMW 530 worth a total of a RM1.5 million in a bid to lure Facebook users to a fanpage used to denounce Bersih.
After three months, the Facebook fanpage could only attract 1,437 "likes", dismally short of Jamal's target of 150,000.