Mayor Eric Adams is praising a new federal directive to regulate the sale of unfinished firearms, also known as ghost guns.

These partially built firearms have become more popular in recent years since buyers can bypass background checks to purchase guns. Ghost guns also typically lack serial numbers, making them difficult to track.

The Bureau of Alcohol, Tobacco, Firearms and Explosives sent a letter to all federally licensed firearms dealers this week instructing them to follow the same steps for ghost gun sales that they do for sales of other firearms, even if a gun was only partially assembled and could be "readily" completed. That means people who try to buy almost-complete firearms at a licensed gun store will have to undergo a background check. Dealers will also need to mark ghost guns with serial numbers, so that law enforcement can keep track of them.

“I applaud the Biden-Harris administration, and ATF specifically, for taking this common-sense step to regulate the sale of deadly weapons and close this long-standing loophole that has contributed to the increase in violent crime across the country,” Adams said in a statement on Wednesday. “We know that nothing can bring back the victims of gun violence, but this action will help spare more families the heartbreak of losing a loved one to these deadly and untraceable weapons.”

The mayor filed lawsuits against five companies that sell ghost guns online earlier this year. Four of the distributors have since agreed to stop doing business with New York City residents as part of settlements.

Attorney General Letitia James has also sued 10 ghost gun distributors after ordering them to stop marketing and selling to New Yorkers. The state made it illegal to possess or sell ghost guns and unfinished firearm frames last year.

New York law enforcement has recently made it a priority to confiscate illegal ghost guns and prosecute those who are buying and selling them. The NYPD has seized more than 430 ghost guns this year, according to the mayor’s office. That’s up from 17 in 2018.

A ghost gun has also been connected to the killing of 16-year-old Angellyh Yambo, who was shot outside her high school in the Bronx this past spring.

In April, the U.S. Department of Justice updated its definition of the word “firearm" to include unfinished pistols that would only require a small amount of time and effort to complete. That rule took effect in August. The new memo from the ATF is meant to clear up potential questions from the gun industry about how the new regulations should be applied.

In a press release, ATF Director Steven Dettelbach called the letter an “an important step” in regulating the sale of ghost guns.

“Ghost guns can kill like other firearms if they are in the wrong hands, so they are treated as firearms under the law,” he said.