Mayor Bloomberg said graffiti art like the works being painted throughout New York City by secretive artist Banksy should not be permitted because they deface property and contribute to urban decay.
The British artist has been decorating city streets with his works, mostly graffiti paintings, in what he says on his website is an artist's residency here.
On Tuesday in Tribeca he left a painting of the World Trade Center towers, adorned with a flower at the site where the north tower was struck by a plane.
The works have been known to draw crowds. Two enterprising locals reportedly blocked off one piece in East New York and charged art lovers to see it last week.
The billionaire mayor told reporters Wednesday that graffiti ruins property "and is a sign of decay and loss of control."
"Nobody's a bigger supporter of the arts than I am," he said. "I just think there are some places for art ... and you running up to somebody's property or public property and defacing it is not my definition of art," he said.
"Or it may be art but it should not be permitted," he added.
On Wednesday, Banksy left a work of sculpture in the South Bronx. The fiberglass sculpture of Ronald McDonald will appear outside a different McDonald's every day at lunchtime for the next week, his website said.