SPRINGFIELD, Ill. — The Illinois Supreme Court has upheld the state’s ban on the sale or possession of the type of semiautomatic weapons used in hundreds of mass killings nationally.

In a 4-3 decision Friday, the high court found that the Protect Our Communities Act does not violate the federal Constitution’s guarantee of equal protection of the law nor the state constitution’s bar on special legislation.

The court also decreed that state Rep. Dan Caulkins, a Decatur Republican, a Decatur pawn broker and like-minded Macon County gun-owners who brought the lawsuit had earlier waived their claims that the law infringes on the Second Amendment to own firearms and could not raise it before the Supreme Court. It’s a claim Caulkins’ attorney vehemently denies.

The Second Amendment claim is alive, however, in several federal lawsuits filed in southern Illinois, later consolidated and awaiting appeals court action.

The law bans dozens of specific brands or types of rifles and handguns, .50-caliber guns, attachments and rapid-firing devices. No rifle is allowed to accommodate more than 10 rounds, with a 15-round limit for handguns. The most popular gun targeted is the AR-15 rifle, which can be found in at least 25 million American households, according to 2021 research by Georgetown University.

But it carves out exceptions. Those who possessed semiautomatic guns before it became effective on Jan. 10 are allowed to keep them but must register them with the state police by Jan. 1, 2024. And seven categories of “trained professionals,” such as police officers, active-duty military, corrections officials and qualified security guards, may carry them.

Bolstered by the 2022 U.S. Supreme Court case that determined Americans have a right to carry weapons in public for self-defense, Caulkins argued that the plaintiffs and those granted exemptions to the ban are “similarly situated” in that they all hold required Firearm Owners Identification Cards and are protected by the Second Amendment, but were not given equal protection of the laws when the ban was applied to them.

Justice Elizabeth Rochford, writing for the majority, countered that in the case of grandfathered gun owners, there’s no dissimilar treatment. And just having a FOID card doesn’t mean a gun owner has arrest powers or other duties assigned to the trained professionals, nor the training and experience with the firearms they carry.

“The equal protection clause guarantees that similarly situated individuals will be treated in a similar manner, unless the government can demonstrate an appropriate reason to treat those individuals differently,” Rochford wrote. “The equal protection clause does not forbid the Legislature from drawing distinctions in legislation among different categories of people as long as the Legislature does not draw those distinctions based on criteria wholly unrelated to the legislation’s purpose.”

Caulkins’ attorney, Jerrold Stocks, said additional legal action was likely, including a potential appeal to the U.S. Supreme Court.

Democratic Gov. J.B. Pritzker signed the Protect Our Communities Act hours after lawmakers sent it to him in a lame-duck session in January, months after a shooter using a high-powered rifle killed seven and injured dozens on Independence Day 2022 in the Chicago suburb of Highland Park. The new law set off a firestorm of criticism from gun-rights advocates, including county sheriffs who were nearly unanimous in signing a statement that they would not zealously enforce the law.

“This is a commonsense gun reform law to keep mass-killing machines off of our streets and out of our schools, malls, parks, and places of worship,” Pritzker said in a statement. “Illinoisans deserve to feel safe in every corner of our state — whether they are attending a Fourth of July Parade or heading to work — and that’s precisely what the Protect Illinois Communities Act accomplishes.”

The court’s fifth Democrat, Justice Mary K. O’Brien, dissented, deciding the law is illegal special legislation that gives some of the excepted classes — retired police officers, for example — rights to the weapons, without rationale, that the plaintiffs don’t have.

The court’s two Republicans, Justices Lisa Holder White and David Overstreet, filed a separate dissent. They found that lawmakers so blatantly violated the constitutional procedures for approving legislation as to make the law unconstitutional, “thereby obviating the need to address the firearm restrictions at issue in this appeal.”

“Important as this case is, constitutionally embedded process matters,” Holder White wrote. “Where the Legislature fails to honor our constitutionally mandated process, this court is duty bound to adhere to our constitution and require the Legislature to do the same.”