Paragraph 7(3)(c.1), and then there are a couple of portions of that. There are different ways you can use lawful authority. One of them is what Mr. Martin cited, but there are others.
It's been indicated that the government agency asking for the information “suspects that the information relates to national security, the defence of Canada or the conduct of international affairs”, but those aren't the only circumstances in which information can be asked for where lawful authority is cited without a search warrant.