The U.S. Supreme Court agreed Tuesday to consider a challenge to Cook County’s ban on assault weapons, setting the stage for what could be a crucial ruling on the right of people to own the types of firearms that have been used in mass shootings.

Cook County’s ordinance prohibits the possession, acquisition and transfer of the weapons in question. It applies to 125 prohibited rifles, such as AR-15s.

But gun-rights advocates say only “dangerous and unusual weapons” can be banned under the Second Amendment — and firearms “in common use” by law-abiding citizens “cannot be unusual.”

A 2022 Supreme Court ruling laid out a two-step test for such gun laws. In New York State Rifle & Pistol Association v. Bruen, the justices held that if an individual’s conduct is covered by the Second Amendment, the government must then demonstrate that the law is “consistent with this nation’s historical tradition of firearm regulation.”

Certain Supreme Court justices have since shown an interest in considering a law like Illinois’. Justice Clarence Thomas wrote in 2024 that, if the 7th U.S. Circuit Court of Appeals “ultimately allows Illinois to ban America’s most common civilian rifle, we can — and should — review that decision once the cases reach a final judgment.”

Thomas’ comment was in reference to Illinois’ separate assault weapons ban, a signature achievement of Gov. JB Pritzker that for years has been the subject of litigation in the federal courts. Pritzker signed the ban into law in 2023 following the 2022 Highland Park parade shooting, which left seven dead.

The Highland Park gunman used an AR-15-style semiautomatic rifle.

This is a developing story. Check back for updates.