Wisconsin -

The Madison-based Freedom From Religion Foundation is speaking out against a letter from Green Bay's mayor inviting Pope Francis to the area.

Mayor Jim Schmitt has invited the pope to make a pilgrimage to the Our Lady of Good Help shrine in New Franken, the only site of a recognized apparition of the Virgin Mary in the United States.

Freedom From Religion Foundation co-presidents sent a letter to Schmitt, saying it is a "shocking" breach of civil and secular duties as mayor.

The foundation cites the "Pope to Green Bay" petition website created by the city. An FFRF attorney has made an open records request for documents related to the invitation.

Pope Francis is scheduled to visit the United States in 2015. Vatican sources have said he plans to visit Philadelphia during the trip, but there is no set itinerary at this time.

The Freedom From Religion Foundation previously filed suit forcing the city of Green Bay to stop putting up a nativity scene at City Hall.

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Freedom From Religion Foundation Protesting Pope Invitation