Jodie Emery says "Cannabis Day" has been held for nearly 20 years and typically attracts about 10,000 people who sell, buy and smoke illegal marijuana in the public square.
But she says she and her husband, pot activist Marc Emery, received a letter from deputy city manager Sadhu Johnston earlier this month telling them to stop planning the event because they don't have a permit.
Emery says organizers have never sought a permit because the annual event is a protest, not a festival, and volunteers previously paid for toilets, security, radios and first aid at the city's request.
A larger marijuana protest held annually on April 20 attracted tens of thousands of supporters this year and sent 64 people to hospital with symptoms including nausea and heart palpitations.
Vancouver Police Const. Brian Montague says officers will prioritize the safety of the public, police and protesters at the event and will conduct enforcement when necessary.