In what is being called a precedent-setting case, a Toronto man is being prosecuted for criminal harassment for messages he allegedly posted on Twitter.

A woman who cannot be named alleges Gregory Alan Elliott sent her messages through the social network and would not stop when asked. She says she feared for her safety during the period he sent the messages.

He is also accused of sending Twitter messages to two other women, who found them to be derogatory and threatening. He allegedly called the women "fascist feminists."

Elliott was charged by police two years ago. The court case is scheduled to begin on Tuesday in Toronto.

"To my knowledge, this is the first time that somebody has been charged for behaviour that is exclusively on Twitter," said Gil Zvulony, a Toronto internet lawyer specializing in defamation, in an interview with Matt Galloway on CBC-Radio's Metro Morning.

Harassment is generally defined as any communication that is unwanted and there is a threat associated. Twitter is a form of communication, so because messages may have come over Twitter, it makes no difference to the charge, said Zvulony.

"There is no real immunity because you are doing it on Twitter," he said. "Theoretically, someone's behaviour on Twitter could land them in jail."

Even though cases of harassment are rare on Twitter, social media and the law are becoming more intertwined.

"Social media, or anti-social media, as I like to call it sometimes, is coming up all over the place," said the lawyer. "Facebook messages are introduced in court all the time. What someone says on Twitter could be the subject of a defamation lawsuit."

But the line between harassment and general 'trolling,' or taunting, goading, pestering or bothering another Twitter user can be blurry. Zvulony said that may come up in this trial.

"The behaviour has to be objectively offensive," he said. "When it comes to Twitter, there is a lot offensive behaviour happening on Twitter all the time. It's sort of par for the course. It's interesting to see in this case how much that norm on Twitter translates into [the notion] that this complainant should not have felt threatened."

Zvulony said that the only real test for whether something should be posted on Twitter is to say it out loud.

"If you're not going to say it in a crowded room directly to the person, don't say it on Twitter."