Becerra set a precedent. 

Via NJ.com: 

New Jersey's attorney general on Tuesday sent warning letters to manufacturers of unregistered "ghost guns" as state lawmakers pursue a formal ban on the sale of firearm parts used to make untraceable homemade guns.

"These weapons are illegal in our state," Attorney General Gurbir Grewal wrote in the letter. "Your actions violate the laws of New Jersey and, if you do not stop these activities within 15 days, I will bring legal action against your company."

The letter targeted companies advertising online for the sale of "unregistered and unserialized firearms -- including assault weapons -- constructed, at least in part, by the purchaser."

It is unclear which companies were sent the warning. Grewal's office declined to disclose the names of the letter's recipients and would not say how many letters were sent.

"We are not releasing any additional information at this time, as we hope these companies will comply with our cease and desist letter," said Lee Moore, a spokesman for the attorney general. "Should they fail to do so, we will be initiating public legal action against them."

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