2 ghost gun retailers agree to stop selling parts, kits to New York City residents

• Rainier Arms and Rock Slide USA did not immediately respond to Axios' request for comment.

Details: Rainier Arms agreed to permanently stop selling all unfinished frames or receivers to New York City customers and to remove such products from its online store, according to NBC.

• It also agreed to hand over documents regarding sales in the city since February 2020.

Why it matters: The Wednesday settlement came the same day a federal ruling went into effect requiring background checks for ghost gun purchasers and for kits to include serial numbers.

The big picture: Ghost guns, which are untraceable firearms that are becoming more prevalent in the U.S., have posed a challenge to law enforcement since they don't have serial numbers, making them difficult to track.

• President Biden announced the new rule in April to regulate ghost guns and make them harder to obtain.

By the numbers: In 2021, some 20,000 suspected ghost guns were recovered in criminal investigations throughout the U.S. — that's a tenfold increase in just five years, according to government data.

Flashback: Polymer80, one of the largest manufacturers of ghost guns in the U.S., was permanently barred earlier this month from selling unserialized, untraceable firearms to Washington, D.C. residents.

• The judge in that case also ordered the company to pay more than $4 million in penalties for making false and misleading claims about the legality of its products, according to the D.C. Attorney General's Office.