New Jersey's attorney general has sued a California company that sells gun parts that can be turned into working firearms.

The suit announced Friday alleges that U.S. Patriot Armory, based out of Apple Valley, California, violated New Jersey's consumer fraud laws when it advertised and sold gun parts to an undercover investigator last month.

“We wanted to see what they would do when they thought no one was looking,” Attorney General Gurbir Grewal said.

The investigator bought parts for an AR-15 assault rifle.

The lawsuit seeks civil penalties and to stop the company from shipping parts to New Jersey.

“These civil penalties include $10,000 for the first offense and $20,000 for each subsequent offense,” said Paul Rodriguez with the New Jersey Division of Consumer Affairs.

New Jersey bans purchases of gun parts for use in making firearms with no serial numbers, called "ghost guns." It's also a crime to possess an unregistered assault firearm in the state.

New Jersey banned the purchases last year.

Grewal said that this is the first lawsuit by a state against a “ghost gun” seller. He said that 16 companies that were known to sell the gun parts were sent cease and desist letters after the practice was outlawed in New Jersey. He says that 15 of them complied.