On Oct 20, University of Toronto student Derek Laventure attended a protest outside the Ontario Tory convention. He saw a police officer drag away a fellow activist and he was heard to say, "That's not right." Next, witnesses say, he was brutally assaulted by several police officers, thrown against a barricade headfirst (his eye was so bruised, it swelled shut), and arrested.

His crime? Allegedly carrying a weapon and using it to assault a police officer. The "weapon" was a black flag.

On the night Mr. Laventure was arrested, Elan Ohayon, a U of T PhD student, was sleeping in Toronto's Allan Gardens. He had camped there every Friday for more than a year as part of a protest against inadequate public housing and police harassment of homeless people. The next morning, Mr. Ohayon woke up surrounded by police officers. They arrested him and, he alleges, assaulted him. Like Mr. Laventure, Mr. Ohayon was charged with assaulting police. He was told to sign bail conditions that barred him from returning to Allan Gardens. He refused. That meant abandoning the vigil to which he had committed himself as an activist.

Last week, after spending 20 nights in jail, a judge struck down the conditions placed on Mr. Ohayon's release. A few hours later, he was once again camped out at Allan Gardens.

It isn't the first time in recent months that a judge has questioned bail conditions that restrict the right to engage in political protest. After an anti-poverty protest at Queen's Park turned violent last June, several of the key organizers of the Ontario Coalition Against Poverty were charged with inciting or participating in a riot. Though they had not been convicted of any crime, their bail conditions explicitly barred them from continuing to be part of OCAP: They weren't allowed to communicate with anyone in the organization, to go to any demonstrations, to go near Allan Gardens or to Queen's Park.

For OCAP organizer Stefen Pilipa, who had to leave the group and take a job at a factory after his arrest, the net effect was that "we were fired—by legal means—from the job that we do."

Only as it turns out, the police, in their efforts to hobble OCAP, violated the protesters' rights. In September, a higher court overturned most of the bail conditions on the grounds that they restricted "peaceful and lawful protest."

In Montreal, two days after Mr. Ohayon's arrest, another activist was facing allegations that participating in a protest is a criminal offence. After the G20 summit in Montreal, Jaggi Singh was arrested and held for 48 hours, though he did nothing more than hand out leaflets and give a speech. In court, a police officer testified that Mr. Singh's speech "incited a riot" (he was not charged with this offence in the end).

What did Mr. Singh say? He asked some difficult questions about the real cost of the economic policies pursued by the politicians at the summit. What is violence, he asked—a broken window at a demonstration, or the violence of homelessness, social exclusion, and police brutality?

What links the crackdowns on activism in Quebec and Ontario is that, increasingly, people such as Mr. Singh and Mr. Ohayon are facing the same kind of exclusion and criminalization they are agitating against: In trying to fight the problem, they are getting a taste of it firsthand. The fear that a protest might turn violent is being used to justify staffing demos with more cops than protesters; photographing activists; arresting leaders off the street; and demanding bail conditions that make activism illegal. As well, says Bob Kellerman, lawyer for several of the protesters, "when police use excessive force, they have to justify it by accusing people of such things as assaulting police."

The net effect is that some of the most effective organizers in the country are spending precious time trying to keep themselves from being convicted of crimes they should never have been charged with in the first place.

Mr. Kellerman says minor charges such as trespass are routinely being inflated to criminal charges, "to provide a legal basis for arrests and restrictive bail conditions they would not otherwise be able to justify. The police view each demonstration as trouble rather than as a sign of a healthy democracy."

No wonder, then, that there is a widespread perception among activists that police are waging a war against them. Two weeks ago, Quebec Public Security Minister Serge Menard gave a preview of his plans for containing protests during the Summit of the Americas, to be held in Quebec City in April. "If you want peace," he said, "prepare for war."

This article first appeared in The Globe and Mail.