Red-shirt leader Nattawut Saikuar has offered advice to young protesters, warning that their violent confrontations with authorities could end up with a win for those in power.
"Please think it through thoroughly," he said on Friday in a message broadcast live on Facebook announcing a peaceful car rally calling for the resignation of Prime Minister Prayut Chan-o-cha.
"I think you don't want to see the armed forces coming out. As for those in power, I am not so sure. You'd better watch your game carefully," he said.
Mr Nattawut's message follows a series of street rallies in Bangkok organised by students and their allies that ended with violence. Police fired rubber bullets, water cannon and tear gas at the demonstrators, who replied angrily with rocks, ping-pong bombs and giant firecrackers.
Rallies culminating in violence could be playing into the hands of those in power, he warned.
Police are under criticism for using rubber bullets and tear gas against protesters, but Metropolitan Police Bureau chief Pol Lt Gen Pakapong Pongpetra has insisted this is the best strategy to curb violence by protesters.
The city police chief on Wednesday called for soldiers to help quell clashes but an armed forces source said troops may be used only to protect key locations, leaving police to handle the demonstrations.
Mr Nattawut is due to lead a car parade starting at 3pm on Sunday, calling for Prayut Chan-o-cha to resign from the prime ministership.
The rally plans to move along three routes, one from Ayutthaya to Lat Phrao intersection led by activist Sombat Boonngam-anong.
The red-shirt leader pledged that the vehicle rallies would be peaceful events and would end with motorists tooting car horns from the start to the end of the national anthem at 6pm.
He said the parades would avoid places such as Government House and the prime minister's residence that could be used by security authorities as an excuse for violent measures against protesters.
