Police in St. Petersburg have been ordered to crack down on opposition rallies set to coincide with President Vladimir Putin’s birthday Oct. 7.

Presidential hopeful Alexei Navalny urged supporters to take to the streets on Putin’s birthday this Saturday, despite being jailed for 20 days last weekend for organizing unauthorized campaign events.

“The police will act very harshly,” an unidentified source familiar with the government’s planned response, told the Interfax news agency.

Navalny’s staff called for protests in 80 Russian cities Oct. 7. St. Petersburg, where Putin was born and raised, is slated to be the epicenter of the scheduled demonstrations.

“Any provocations and illegal actions in the city center will be stopped in the strongest possible way.”

St. Petersburg municipal authorities have rejected more than 10 applications to hold events with Navalny this Saturday, according to Interfax.

Navalny’s local campaign coordinator was detained during searches at the presidential hopeful’s St. Petersburg headquarters on Tuesday.

The opposition politician announced his intention to run for presidency next March despite a criminal conviction that bars him from participating and which he says is politically motivated.

Local media later reported that the Field of Mars, where the demonstration is scheduled to take place, was cordoned off with emergency tape and fencing for what authorities claim are planned renovations.