The city is suing 15 out-of-state gun shops it says supply a significant portion of the guns that flow into New York, including some that end up in the hands of criminals.

The lawsuit being filed Monday asks the federal court to order supervision and extra training for the dealers in Georgia, Ohio, Pennsylvania, South Carolina and Virginia. It also seeks some damages and compensation.

"By and large, most gun dealers respect and follow the law, but the small group of dealers that do not should be held accountable," Mayor Michael Bloomberg said in a statement.

The city's law department singled out the 15 gun shops after hiring private investigators who fanned out to dealers in the five states over the past several weeks.

Wearing hidden cameras, the investigators entered stores in teams of two and attempted "straw purchases," in which the buyer completes the paperwork and passes the background check, but later hands over the weapon to someone else who is not allowed to own a firearm.

The scam, prohibited by federal law, is typically used by people who are under 21 or convicted felons. The 15 dealers named in the suit sold guns to the undercover investigators. The city said the sales were refused at about 30 other shops.