MONTREAL - The City of Montreal might be facing a class action lawsuit over how it handled a massive kettle during student demonstrations.

The largest mass arrest by far during the student conflict, on May 23, 500 people were arrested at the corner of Sherbrooke and St-Denis Sts. in a police kettling operation.

They said they were detained for hours with their hands tied behind their backs, with no access to water or to washrooms.

Some people said they were forced to urinate on the floors of the city buses they were being kept in.

Those detained also said they were kept in appalling conditions, despite never being told on what grounds they were being arrested.

After about seven hours, they were given tickets for disturbing the peace.

Last Friday, lawyer Marc Chetrit filed a motion for certification of a class action.

Chetrit said he and his client believe the arrests were illegal, because they appear to have been planned in advance.

“The (Surete du Quebec) was present. They’re not always present. There were buses at the ready to bus the people who were kettle to the (police) operational centre. We also know that in social media the day before, there was an anonymous tip off that there may be something planned, or in the making, the next day,” he said.

Chetrit also said many of the people arrested on May 23 were not participating in the student protest, and were simply bystanders.

He also argued the fact that people weren't told why they were being arrested violates basic rights and freedoms.

He would not reveal how much money the group is seeking, and that information has not yet been made public.

The class action suit must be approved by superior court before it is heard.