The Supreme Court of Canada will hear an appeal Tuesday on whether a drug-sniffing dog inside a school in a southwestern Ontario city went beyond the reasonable limits of police powers.

During an unexpected police visit to St. Patrick's High School in Sarnia, a trained police dog sniffed out a backpack containing marijuana and magic mushrooms, leading to trafficking charges against a youth known only as A.M.

At issue is whether the actions that led to the charges breached Sec. 8 of the Charter of Rights and Freedoms covering what constitutes reasonable search and seizure.

In 2004, the Ontario Court of Appeal upheld a previous trial judge's decision to acquit the youth, calling it a warrantless random search after police admitted they didn't have grounds for getting a search warrant beforehand.

Crown lawyers will argue the sniffer dogs didn't constitute a search, and that they only provide information that could lead to one.

They will argue that smells in public air aren't private and compare it to officers detecting an odour in the air.

But opponents say it's more intrusive and allowing such techniques could lead to widening the powers of police to conduct random searches in public places such as churches, schools and shopping malls.