Vancouver police have issued an unusual plea for motorists to avoid the city's downtown core at the height of rush hour this Friday.

Police are anticipating major traffic jams due to the monthly bike rally known as Critical Mass, which sees hundreds of cyclists converge on the Vancouver Art Gallery before taking over major streets, blocking traffic and frequently causing angry confrontations with motorists.

With increased traffic expected as a result of the August long weekend, police are now urging drivers to steer clear in case downtown becomes paralyzed.

"Fights, assaults, road race incidents. No one wins when these violent incidents occur," Vancouver Police chief Jim Chu said.

While Vancouver mayor Gregor Robertson is an avid cyclist, he feels that the monthly rally may be getting out of control.

"I don't support it in it's current form right now," Mayor Gregor Robertson said. "I want to see change. I want to see the ride be a celebration."

Police say the protestors' rights are protected and that organizers are hard to track down.

Amy Walker has participated in the protest ride before, and says it's designed not to have any organizers.

"It's a leaderless ride," Walker said. "They go wherever the ride goes."

She says it's just a way to promote biking.

"Does it cross a line when it shuts a city down? You could say that about any traffic jam," she said. "Is it illegal for car drivers to drive at the same time? It's a bunch of cyclists riding on the street."

Police don't plan on ticketing many of the riders, saying it could just increase hostility.

With a report from CTV British Columbia's Norma Reid and files from The Canadian Press