A case in which police handcuffed and charged a woman after she refused to hold an escalator handrail in the Montreal subway system has prompted the Supreme Court to raise standards for police conduct and to tell Canadians they need not obey an officer’s unlawful commands.

The court — sharply disagreeing with two lower courts in Quebec — granted Bela Kosoian a victory in her lawsuit against Laval Constable Fabio Camacho, the City of Laval and the Montreal subway authority. The unanimous court awarded her $20,000.

The ruling has implications for the daily interactions between police and other Canadians. Police can be sued, the court said, even if they act in good faith and in accordance with their training, as Constable Camacho did. They need to ensure they act reasonably, while keeping the liberty rights of Canadians in mind. (The ruling does not, however, mean they can be sued if a constitutional ruling changes how a law is interpreted, the court said.)

“In a free and democratic society, police officers may interfere with the exercise of individual freedoms only to the extent provided for by law,” Justice Suzanne Côté, one of three Quebec judges on the court, wrote in the 9-0 ruling.

Ms. Kosoian told The Globe and Mail that she spent 10 years on her legal battle “because the rule of law has to prevail. It was an obvious abuse of power. If police do not know the rule of law, what do you think, is it dangerous or not?" She said the 2009 incident has left her with fears that have still not gone away.

Cara Zwibel, a lawyer with the Canadian Civil Liberties Association and an intervenor at the Supreme Court, said that before the case, it was unclear whether police acting in good faith could be held responsible in civil court for their actions. The ruling makes clear, she said, that the standard is whether police acted reasonably, in accordance with the law.

The CCLA was especially pleased that the court told Canadians they do not have to identify themselves when asked to by an officer who is acting unlawfully.

A spokesman for Laval and the officer said they are still analysing the ruling and are not ready to comment.

In May, 2009, as Ms. Kosoian, then 38, headed to her university classes in international law, she ignored a yellow “Hold Handrail” sign while looking for money to buy a ticket in her backpack. She also ignored repeated commands from Constable Camacho to use the handrail. Then, when the officer told her to stop and identify herself, she declined to do either. He and a colleague then held her by the elbows and brought her to a small room where Constable Camacho put handcuffs on her, with her arms behind her back.

Police charged her with violating a bylaw by failing to hold the handrail — which carries a fine of $100 — and with hindering them in their duties (a $320 fine). A Municipal Court judge dismissed both charges, saying it was not clear that the holding of the handrail was a legal obligation.

Two lower courts dismissed Ms. Kosoian’s lawsuit against the subway system, City of Laval and Constable Kamacho. Quebec Court Justice Denis Le Reste said Constable Kamacho’s conduct had been “exemplary and irreproachable,” while Ms. Kosoian’s behaviour was “inconceivable.” Quebec’s highest court — the Court of Appeal — ruled 2-1 against the lawsuit, saying Ms. Kosoian had violated a bylaw. Even the dissenting judge said Ms. Kosoian bore 25 per cent of the blame for what happened.

But the Supreme Court said the bylaw created no offence; the yellow sign was a warning, not a directive. It also said she bore none of the blame.

Average citizens may wish to be cautious and comply with police, it said; if they don’t, they run a risk that they could be charged with willfully obstructing an officer. But “a well-informed person does not commit a civil fault merely by refusing to comply with an order that proves to be unlawful,” Justice Côté wrote. “A person whose rights are infringed must be able to respond — within reason, of course — without being held civilly liable.”

Bryant Mackey, a lawyer with the Vancouver Police Department, said the ruling is a useful reminder to police services of the importance of knowing and understanding the law, at a time when the law has become increasingly complex.

"The case signals the importance of ongoing education and training of police as a key feature of contemporary operational policing,” he said in an e-mail.

Our Morning Update and Evening Update newsletters are written by Globe editors, giving you a concise summary of the day’s most important headlines. Sign up today.