In Caldara v. City of Boulder, No. 18-1421, 2020 WL 1814596 (10th Cir. April 10, 2020), plaintiffs challenged the constitutionality of a local ordinance regulating the sale and possession of 10th Circuit Spotlightfirearms. The federal district court abstained from exercising its jurisdiction. The Tenth Circuit affirmed this discretionary decision under Railroad Commission of Texas v. Pullman, 312 U.S. 496 (1941), concluding that the district court properly abstained and stayed the federal proceedings pending resolution of important state-law issues.

Boulder's Firearms Ordinance

In May 2018, the Boulder City Council passed Ordinance 8245, which prohibits the sale or possession of assault weapons and large-capacity ammunition magazines within the city. The Ordinance also raised the legal age for possession of any firearm from 18 to 21.

Plaintiffs, citizens of Boulder and entities with various interests in the sale or possession of firearms within Boulder, sued the city in federal district court, alleging that the Ordinance violates the U.S. Constitution, the Colorado Constitution, and Colorado state statutes.

After plaintiffs sued in Caldara, different individuals and entities sued in Colorado state court challenging the constitutionality of the same Ordinance. Chambers v. City of Boulder, 2018-CV-30581 (Colo. D. Ct., Boulder Cty. June 14, 2018). The plaintiffs in Chambers challenged the Ordinance under Colorado state law, leaving out any claims under the U.S. Constitution.