PARIS — “Liberté, Égalité, Fraternité” is not just France’s motto, it is the law. In fact, the nation’s highest constitutional tribunal decreed on Friday, it can now be a defense against prosecution.

In a landmark decision, the Constitutional Council said that a French farmer was not guilty of a crime when he smuggled migrants into the country because he acted under “the principle of fraternity.”

The national motto is enshrined in the Constitution in two places, the council noted, which trumps the statute making it a crime to help someone enter the country illegally.

The council’s ruling came in the case of Cédric Herrou, an olive grower, who was charged with shepherding migrants across the French-Italian border and into southern France’s Roya Valley.