From Guns.com:

Grewal’s action targets unnamed “ghost gun makers” who he argues advertises build and kits to New Jersey residents with possible civil action under New Jersey’s Consumer Fraud Act, with as much as a $10,000 penalty for initial offenses. He holds that fraud is committed because the makers do not disclose that possessing a firearm classified under state law as an unregistered “assault weapon” in New Jersey is a crime.

“As the chief law enforcement officer for New Jersey, I demand you stop selling and advertising unregistered and unserialized assault weapons to New Jersey residents,” Grewal says in the letter. “Should you fail to comply with this demand within 15 days, my Office will initiate legal action.”