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"We wanted to say we are against the rise of nationalism and authoritarianism in France and in other countries," the advocacy group's head in France Jean-Francois Julliard told public radio station Francinfo.
This is our way of reminding everybody they all need to mobilise to defend these values of Liberty Equality and Fraternity."
Le Pen faces off against centrist Emmanuel Macron in the May 7 ballot.
Macron is tipped in polls to win and become France's president for the next five years.
The Greenpeace action came on the last day of campaigning.