SPRINGFIELD, Ill. — Gov. J.B. Pritzker authorized state regulation of firearms dealers Thursday in a reversal of his predecessor’s policy and prompting a gun owners group to threaten legal action against Illinois.

Pritzker, sworn in on Monday, chose an elementary school in Chicago to sign legislation meant to cut down on illegal purchases of firearms through video monitoring, tighter inventory control and gun-shop employee training.

“We can prevent someone from buying a gun for someone else who is not legally allowed to own a gun,” said Pritzker, standing next to Chicago Police Superintendent Eddie Johnson, whose force confiscated 10,000 illegal guns last year. “Many of the incidents of gun violence that occur in our city and all across our state occur with illegal guns.”

“The action taken today is another assault on our 2nd Amendment rights.”

– Richard Pearson, Illinois State Rifle Association

The law affects about 2,400 firearms dealers and its provisions take effect in six months. Each must show it is licensed with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives and purchase a five-year state permit — $1,500 for retail shops and $300 for independent dealers. Each must install videotaping in retail sections of the store, maintain an electronic inventory and require annual employee training in spotting so-called straw purchases.

The Illinois State Rifle Association promised a lawsuit challenging the plan.

“The federal government already licenses gun dealers. There is no need to add yet another layer of bureaucracy on gun dealers,” executive director Richard Pearson said in a statement. “The only thing this measure is going to do is make it cost more money for gun dealers to do business in Illinois, which is going to hurt the smaller dealers.

“The action taken today is another assault on our 2nd Amendment rights.”

Pritzker, who already this week reversed course on GOP Gov. Bruce Rauner’s policies toward labor with pro-union action, said gun-rights organizations are “just wrong” in their criticism of the licensing bill. He added, “I’m going to continue to make sure that we’re standing up to the voices like the Illinois State Rifle Association and the National Rifle Association to protect our families and our children.”

Lawmakers endorsed the idea twice last year. Rauner vetoed the first version in March. Democrats who control the General Assembly, led by Sen. Don Harmon of Oak Park, OK’d it again in May but never sent it to Rauner for consideration.

“You don’t need a Ph.D. from Harvard to figure out that if you’re going to regulate a barber shop and a bar, maybe you should regulate a gun dealer.”

-Chicago Mayor Rahm Emanuel

“Thank you for figuring out in four days what some other people couldn’t figure out in four years,” Chicago Mayor Rahm Emanuel said to Pritzker. “You don’t need a Ph.D. from Harvard to figure out that if you’re going to regulate a barber shop and a bar, maybe you should regulate a gun dealer.”

Harmon, who first introduced the idea in 2003, said the law is more about allowing the state to gather information on straw purchases through video monitoring and electronic inventory and sales records than it is about punishing dealers. While the ATF audits gun shops, Harmon said the federal agency has fewer than two dozen agents to oversee all of Illinois’ dealers. He contended audits occur only once every three to five years and only verify whether a gun is in the dealer’s inventory or has been sold, not examining patterns or regularity of purchases.

“We can’t think that this bill, however important it is, is the solution,” Harmon said. “It will help but there’s more work to be done.”