TORONTO - A raucous but peaceful Tamil protest that shut down a major Toronto highway and ended with a phone call from a Liberal official and not through forceful police intervention may cause police to act on future Tamil demonstrations differently, an expert said Monday.

The protesters have taken to Toronto and Ottawa streets many times recently, at one point closing a crucial downtown Toronto street for three days. Their actions escalated Sunday night with an impromptu storming of the Gardiner Expressway.

The disruptive action lit up Internet forums with calls for police to move in and end such demonstrations.

One expert on protest policing said the contentious protest Sunday may cause police to become less accommodating of the group.

"I would guess that their tolerance for these actions are going to go down considerably now," said Patrick Rafail, a doctoral candidate at Penn State University who wrote his master's thesis at McGill University on protest policing in Toronto, Vancouver and Montreal.

"The Gardiner is a major artery. I'm surprised frankly that they didn't move in."

While Toronto police called the action "unlawful" and spoke of the possibility of breaking up the highway protest, in the end they did not. Organizers said they left the highway only after speaking to a Liberal official.

Police chief Bill Blair also credited police negotiations for moving things along.

Ontario's interim Opposition Leader Bob Runciman likened the situation to one in Caledonia, Ont., where aboriginal protesters have been occupying a former housing development site for more than three years.

Many citizens in that southwestern Ontario town are critical of the province, which bought the land from the developer, and the provincial police for not forcibly removing the protesters.

"I think the positions (the Ontario government) have taken have been irresponsible with respect to upholding the rule of law in Caledonia and I think that's compromised them going forward in other situations like the one we've seen here in Toronto," Runciman said Monday.

"When you're blocking a major artery in the city, an economic lifeline for many businesses, I think it's important we send out a message that's not going to be permitted."

Provincial police would also not forcibly remove aboriginal protesters on two occasions in 2007 in eastern Ontario when they blockaded a crucial rail line linking Toronto and Montreal.

In one instance protesters left after negotiating with police, though it was later revealed through wiretaps that provincial police commissioner Julian Fantino warned leader Shawn Brant of consequences if he didn't remove the blockade.

Rafail said in such situations police must weigh many factors. In the protest on Sunday that included the optics of breaking up a crowd that included children, he said.

"They would have had to have used probably some fairly heavy-handed tactics to get people off (the highway)," he said.

"They would have gotten a lot of bad publicity had they gone in with tear gas."

Rafail pointed to past instances of police-protester confrontations that have turned violent, including the 1995 aboriginal protest at Ipperwash Provincial Park, where Dudley George was killed by a police sniper. The fallout from that has resonated for many years, culminating in the release of an inquiry report in May 2007.

The scathing report cited government problems and police insensitivity as contributing factors in George's death.

"Police want to avoid that sort of scrutiny and criticism," Rafail said.

Sunday's impromptu occupation of the highway began as a roving protest through downtown Toronto, but the thousands of Tamil demonstrators burst onto the highway too quickly for police to prevent it and people stayed there for several hours.

It ended around midnight when organizers received a call from Michael Ignatieff's office and a promise the Liberal leader would raise their issue.

Rage and frustration over Sri Lanka's civil war boiled over earlier Sunday after news reports said that an all-night artillery barrage in the country's war zone killed more than 370 people and forced thousands to flee to makeshift shelters along the beach.

The protesters, many of whom say their relatives have been killed in the fighting in their homeland, want Canada to pressure the government of Sri Lanka to accept international calls for a ceasefire.

The police chief called the demonstration on the highway "unlawful," but Blair said he would not take any action that would create an unsafe situation, noting children were among the crowd on the expressway.

Many drivers who were caught in the ensuing traffic jam expressed frustration at the protesters and many other Torontonians took to online discussion boards to voice their anger that police did not break up the demonstration.

"These Tamils will again push the limits of the law and they are now emboldened to keep going," one person wrote.

"They up to now have faced no consequences. If the law does not take care of their illegal activity they may find the patience of the citizens of Toronto growing very thin."

Others expressed sympathy for the plight of people in the protesters' homeland, but did not agree with their tactics.

"Either way, they don't have the right to block our roads to prove their point," another person wrote. "I'd say arrest them all the next time it happens."

At one point police went behind the protest line on the highway and arrested two women and a man. The three face charges of assault on a peace officer and mischief interfere with property.