One of Colorado’s newest and most restrictive gun-control measures is facing a federal lawsuit from the Colorado State Shooting Association, the state’s official National Rifle Association group.

The lawsuit challenges the constitutionality of Senate Bill 3, which was signed into law by Gov. Jared Polis in April. The measure will outlaw the purchase, sale and manufacture of many semiautomatic firearms that use detachable ammunition magazines starting next year.

The Mountain States Legal Foundation filed the challenge Tuesday on behalf of the CSSA and several individual plaintiffs who argue the measure violates their Second Amendment rights by limiting their ability to operate and obtain firearms.

The complaint claims, “because [the law] attempts to govern and regulate arms-bearing conduct, the text of the Second Amendment is implicated.”

Starting in August 2026, the banned firearms will only be available for purchase in Colorado if someone goes through a screening process with their county sheriff to obtain a “firearm safety course eligibility card.” They will also have to go through up to a dozen hours of training and pass a test before they can purchase the banned models.

One part of the law that took effect immediately when it was signed banned rapid-fire trigger devices, like bump stocks, that increase a gun’s rate of fire.

Supporters of the measure argue it will help reduce the amount of damage inflicted during mass shootings. Sen. Tom Sullivan, D-Centennial, was the law’s lead legislative sponsor. His son, Alex, was murdered in the 2012 mass shooting at an Aurora movie theater, in which the shooter used a high-capacity magazine attached to an AR-15.

Sullivan is confident the law will stand up in court.

“We knew this was coming,” said Sullivan, referring to the legal challenge. “This is typical of them, and it’ll end up the way it has been ending up for the last several years. They’ll lose in court and we will move forward on our own to try to figure out what we can do to protect our citizens from gun violence.”

Many of Colorado’s firearm restrictions have faced lawsuits from gun rights advocates in recent years. That includes challenges to the state’s 15-round magazine limit, its three-day waiting period for firearm purchases, and its 21-year-old minimum age requirement for buying guns, all of which have been upheld in court.

Polis’ office, through spokesperson Shelby Wieman, declined to comment on the pending litigation.

“This bill ensures that our Second Amendment rights are protected and that Coloradans can continue to purchase the gun of their choice for sport, hunting, self-defense, or home defense,” Polis said in a statement when he signed the measure into law in April. “I am confident that this bill contributes to improving public safety.”

Gun violence advocacy group Everytown For Gun Safety lists Colorado’s firearm restrictions as the 10th strongest in the country.

This story was produced by the Capitol News Alliance, a collaboration between KUNC News, Colorado Public Radio, Rocky Mountain PBS and The Colorado Sun, and shared with Rocky Mountain Community Radio and other news organizations across the state. Funding for the Alliance is provided in part by the Corporation for Public Broadcasting.