Montreal police used article 500.1 of the province's Highway Safety Code to put an end to the 15th annual anti-police brutality protest on March 15, 2011.
About 150 people who were charged under the code are now arguing that the law is being misused.
Altogether, 239 people were arrested during the 45-minute-long protest.
About a dozen people were fined for disturbing the peace, while most of the others were charged under the Highway Safety Code and subsequently released.
François Van Vliet, one of the people charged, said the law was adopted more than 10 years ago to prevent people from blockading roads with vehicles.
He said this was the first time police used it to stop a demonstration.
The article states " No person may, during a concerted action intended to obstruct in any way vehicular traffic on a public highway, occupy the roadway, shoulder or any other part of the right of way of or approaches to the highway or place a vehicle or obstacle thereon so as to obstruct vehicular traffic on the highway or access to such a highway."
"Clearly, what we're saying is that this law should not be applied to demonstrations," said Van Vliet.
McGill professor Marcos Ancelovici was admitted as an expert witness in the two-week-long court procedure.
He is expected to share his views about demonstrations as a form of freedom of expression.
The outcome of the case will determine whether the article can be used to stop demonstrations in the future.