No food carts were in sight on Sept. 9, when the Harlem Teen Choir serenaded dignitaries attending the opening of the new $65 million plaza in front of the Metropolitan Museum of Art, with its pristine granite fountains and allées of little leaf linden trees.

But the carts were back the next day — growing in number, some days, to more than 20 — vexing museum and city officials.

“What we have now is a blight on a magnificent new civic space, and a huge impediment, bordering on a safety hazard, for the thousands of people who visit the museum every day,” said Harold Holzer, the Met’s senior vice president for public affairs.

The issue is a difficult one, because the vending regulations the city would like to enforce are viewed as somewhat at odds with a 19th-century state law that provides licenses to disabled veterans to vend in certain areas of the city. City officials became so concerned that the growing number of food carts at the Met were not being operated by veterans that they dispatched undercover investigators last year to see if the licensed veterans were actually manning their own carts, according to a recently released report.