An Ontario judge has ruled that hundreds of people detained during the G20 summit three years ago can't sue as a group.

The proposed $45-million class action lawsuit was spearheaded by Sherry Good, a 51-year-old office administrator who says she was corralled by cops for four hours when police in riot gear used a tactic called kettling.

But Friday a judge ruled that it can't proceed as a class action, saying its "broad, sweeping nature" is problematic.

A statement from lawyer Murray Klippenstein's office says they will appeal the decision.