It will soon be much harder for Colorado gun owners to continue purchasing modern semi-automatic firearms.

In a closely guarded ceremony Thursday, Colorado Governor Jared Polis (D.) signed SB25-003 into law. The “Semiautomatic Firearms & Rapid-Fire Devices” bill criminalizes the manufacture, distribution, transfer, and purchase of any semi-automatic rifle, shotgun, or gas-operated handgun that accepts a detachable magazine. The law also carves out an exception from the ban for those who undergo an extensive permitting and training process—the first of its kind for purchasing firearms in Colorado.

“This legislation builds on our commitment to improve public safety, reduce gun violence, uphold our freedom,” Polis said in a statement.

The bill enacts some of the most sweeping gun regulations ever considered in the Centennial State, even compared to the few dozen restrictions Colorado lawmakers have been stacking up over the last decade. It fulfills gun-control advocates’ longstanding goal of cracking down on the availability of certain semi-automatic firearms and is almost sure to draw legal challenges from gun-rights groups.

The Colorado State Shooting Association (CSSA), the state’s NRA affiliate, threatened as much in a statement blasting the Governor’s decision to sign the bill.

“We are resolute in our response,” Ray Elliott, CSSA president, said. “The Colorado State Shooting Association is actively exploring every legal option to challenge this unconstitutional law. Our legal team is preparing to contest Senate Bill 3, and we are committed to pursuing justice through every available avenue.”

The group said it submitted 40,000 petition signatures to the Governor urging a veto earlier this week.

The bill’s controversial nature could explain its unceremonious entry into law. Polis, a Democrat with a libertarian streak, kept his opinions on the policy close to the vest throughout the legislative process. He did not publicly indicate whether he would sign the bill until Thursday, even as he faced immense outside pressure from groups on either side of the issue.

His office did not respond to a request for comment.

While he hesitated to increase public scrutiny of the measure, his office was heavily involved in making the final product less restrictive than its original form. As introduced, the bill envisioned an outright ban on semi-automatic firearms that did not have a permanently affixed magazine capable of holding 15 or fewer rounds—a policy even broader than typical “assault weapon” bans that Polis has expressed skepticism of in the past.

Working closely with the Governor’s office, the bill’s sponsors added several pages to its provisions to craft an entirely novel process for Coloradans to continue purchasing the weapons in question. It includes a prospective buyer having to first obtain a newly established “firearms safety course eligibility card” from their local sheriff, which requires paying a fee, submitting fingerprints, and going through a background check.

Once issued, a firearms safety course eligibility card would be valid for five years. The issuing sheriff would be required to submit cardholders’ data to a newly created “Firearms Safety and Training Course Record System” administered by the Colorado Division of Parks and Wildlife, an agency that currently does not handle anything involving firearm sales.

With a valid eligibility card, a prospective buyer could enroll in either a “basic firearms safety course” or an “extended firearm safety course.” The basic firearms safety course is open to eligible cardholders with a hunter education certification and requires four hours of in-person instruction. Prospective buyers without hunter education training will be required to attend the extended firearm course, which must include at least 12 hours of in-person instruction spread across at least two days.

The bill requires both courses to include curricula on safe weapons handling, secure storage and child access prevention, firearms deaths and mental illness, extreme risk protection orders, and “victim awareness and empathy.” Completing each course would be contingent on receiving a score of at least 90% on a final test.

If a cardholder wants to continue buying the affected firearms, they must undergo the process again after five years.

In addition to restricting the availability of certain guns, the measure also contains provisions going after bump stocks, binary triggers, and similar accessories. It bans the possession of any “rapid-fire device,” defined broadly as any combination of parts that has the effect of “increasing the rate of fire of a semiautomatic firearm above the standard rate of fire.” It also codifies increased criminal penalties for violating the state’s twelve-year-old ammunition magazine ban, now a class 1 misdemeanor punishable by up to a year in jail.

The law’s provisions are set to go into effect on August 1, 2026.