Officials from Denver and the state of Colorado, along with environmental organizations, asked a federal judge anew to throw out a long-running lawsuit challenging the building energy mandates by city and the state in a fight over how far the governments can go in forcing large buildings to cut fossil energy.

The state and the city argued the building energy mandates are necessary to comply with Gov. Jared Polis’ “Greenhouse Gas Reduction Roadmap,” which calls for reaching “net zero” CO2 emissions by 2040.

The latest dismissal motions, filed Oct. 3 by the city, the state and a coalition of environmental intervenors, seek to end the case brought by four trade associations representing apartment owners, hotels and commercial developers.

The Colorado Apartment Association, Apartment Association of Metro Denver, Colorado Hotel and Lodging Association, and NAIOP Colorado have claimed that Denver’s “Energize Denver” ordinance and the state’s “Regulation 28” violate the federal Energy Policy and Conservation Act, which reserves controlling appliance-efficiency standards to the U.S. Department of Energy.

The business groups insisted the rules effectively force owners of large buildings to replace gas-fired boilers and water heaters with electric systems, which the groups claimed is federally preempted.

Denver and the state countered that the case had been filed too late and that the owners lack “standing” — the legal right to sue — because no fines have been imposed and owners have not used the extensions, custom targets or other compliance options available under the rules, and, thus, have not “exhausted” administrative remedies, something the courts usually require for a case to be “ripe” for adjudication.

“The Building Performance Standards rules offer multiple compliance pathways,” the Colorado Energy Office said in a statement, adding that “the BPS (building performance standards) rules do not require electrification.”

Plaintiffs maintained they already face tangible harm through audits, engineering studies and replacement planning needed to meet 2024 reporting deadlines and prepare for 2027 and 2030 targets. Those costs, they said, are immediate and unavoidable.

The trade groups also accused the city and the state of trying to “run out the clock” by relying on procedural defenses, instead of addressing the substance of their claims. They argued the statute of limitations resets each time the rules are amended — most recently when Denver revised its regulations in July 2023 and again in April 2025, each time promising “more flexible compliance options.”

Environmental groups including the Sierra Club, Natural Resources Defense Council, and the Colorado Solar and Storage Association have joined the city and the state, saying the rules are critical to meeting state climate goals and already offer ample flexibility.

Plaintiffs maintained that the flexibility is illusory and that even with exemptions, many buildings will be forced to electrify to meet the city’s and state’s targets.

U.S. District Judge Regina M. Rodriguez will decide whether the motions end the case or allow it to move forward to test whether Colorado’s climate policies conflict with federal energy law.