"The image of David, armed, offends and infringes the law. We will take action against the American company so that it immediately withdraws its (advertising) campaign," Franceschini tweeted in the afternoon.
His comments come after the Historical Heritage and Fine Arts Board in Florence condemned the image by Illinois-based ArmaLite, which uses Michelangelo's statue to promote the huge, $3,000 rifle with the tagline "a work of art".
Curator Cristina Acidini has issued a legal warning telling ArmaLite to immediately withdraw all images Italy deems distort the Renaissance masterpiece.
Italy claims copyright over any images of David, a monumental marble sculpture preserved since 1873 in the Accademia Gallery in Florence. Anyone wishing to commercially use a picture of the statue, the government says, must receive legal authorization and pay a fee -- which ArmaLite had not done.
"The law says that the aesthetic value of the work cannot be distorted," Angelo Tartuferi, director of the Accademia, was quoted by the Republica newspaper as saying.
"In this case, not only is the choice in bad taste but also completely illegal."