Four U.S. cities on Wednesday sued the Justice Department and Bureau of Alcohol, Tobacco, Firearms and Explosives for failing to regulate the sale of “ghost guns” amid a rise in violent incidents tied to the untraceable firearms, which can be built in just hours using online kits.

The lawsuit, by the cities of Syracuse, New York; San Jose, California; Chicago, Illinois; and Columbia, South Carolina, accused the agencies of “arbitrarily” excluding key parts for the guns from their enforcement of the Gun Control Act and allowing gun-building kits without serial numbers to be sold unchecked.