There are two kinds of laws: man's and God's. A man-made code that squares with the moral law, or the law of God, is a just law. But a man-made code that is inharmonious with the moral law is an unjust law. And an unjust law, as St. Augustine said, is no law at all.
Interview in Playboy (January 1965) - Three Ways of Meeting Oppression (1958)