Health Canada sent letters to about 40,000 people across the country to inform them of changes to the Marijuana Medical Access Program beginning April 1. The envelopes referred explicitly to the marijuana program and included users' names and addresses.
Less than a week ago, some complainants came forward arguing that violates their privacy.
The McInnes Cooper law firm filed the class action in Federal Court on Monday.
It must be certified by a judge to proceed, and none of the allegations has been proven in court.
However, a news release from the law firm says: “Health Canada's disclosure of the patients' private medical information has raised serious employment and security concerns, and caused the patients to suffer considerable stress and anxiety.
"We have heard that some individuals have already lost their jobs as a result, and everyone we've spoken with is concerned about their safety in their homes," said lead lawyer David Fraser.
Health Canada issued an apology on its website when the gaffe was first reported and called it an administrative error.