Canada and the United States share an 8891-kilometre undefended border. Refugees who want to enter Canada aren’t allowed to cross the border anywhere they like. They’re supposed to request permission to enter at an official port of entry, like an airport, seaport, or land crossing.

A 20-year-old border agreement called the Safe Third Country Agreement (STCA) sets out the rules. On March 24, it was amended to discourage asylum-seekers from entering Canada illegally.