President Joe Biden took steps on Monday to limit the use of untraceable handguns known as ghost guns, which law enforcement agents say frequently crop up at murder scenes.

Biden proposed new federal laws aimed at privately manufactured firearms that may be constructed from do-it-yourself kits purchased online or in stores. Because the firearms lack serial numbers, tracing the owner is difficult.

“These guns are weapons of choice for many criminals,” Biden said in a Rose Garden ceremony attended by victims and families of gun violence. “We are going to do everything we can to deprive them of that choice and, when we find them, put them in jail for a long, long time.”

The guidelines, which have been in the works for about a year, would specify that unfinished gun kit pieces, such as a handgun’s frame or a long gun’s receiver, will qualify as guns under federal law.

Commercial kit producers will be required to get a license and must include serial numbers on the frame or receiver of the kits. Commercial sellers of the kits will be forced to obtain a license and conduct background checks on potential consumers before making a transaction, exactly like they do now.

Biden also announced that he is proposing Steve Dettelbach, a former United States attorney from Ohio, to be the head of the Bureau of Alcohol, Tobacco, Firearms, and Explosives. The ATF is the government agency in charge of enforcing the country’s gun regulations.

Biden also called on Congress to prohibit the sale and possession of “ghost guns” in addition to the new regulations.

Biden’s initiatives will almost certainly be met with fierce opposition from the gun lobby.

The group urged Congress to use the Congressional Review Act, which permits lawmakers to reject rules made by federal agencies, to stop the rule from going into effect.

The rules were applauded by gun control campaigners.

John Feinblatt, president of Everytown for Gun Safety, said that “Ghost guns look like a gun, they shoot like a gun, and they kill like a gun, but up until now, they haven’t been regulated like a gun.”