The North Carolina Supreme Court on Friday quickly rejected a challenge to regulators who decided a clean-energy advocacy group broke electric-service rules by selling solar power to a church.

The justices heard oral arguments less than four weeks ago in the case involving NC WARN, which installed solar panels on a Greensboro church’s roof and sold electricity to the church at rates below what Duke Energy Corp. subsidiaries charged.

The justices issued a one-word opinion that affirmed the majority decision on a Court of Appeals panel last year and gave no further explanation. That lower-court opinion agreed with a 2016 order by the North Carolina Utilities Commission that NC WARN was acting as a “public utility” subject to its regulation and infringing on Duke Energy’s government-sanctioned utility monopolies.

NC WARN had sought a ruling by the commission as a “test case” involving third-party sales. Its lawyers argued the group didn’t meet the definition of “public utility” because it was only helping nonprofits save money with clean energy.

Duke Energy spokesman Randy Wheeless said the country’s No. 2 electricity company “was confident that the original decision by the North Carolina Utilities Commission was absolutely correct” and was pleased with the swift decision.

Still, a ruling favorable to NC WARN worried utilities for fear they could lose revenues to competitors who cherry-picked customers that used high levels of energy.

NC WARN Executive Director Jim Warren said Duke Energy has been dragging its feet on rapidly expanding solar energy and Friday’s decision doesn’t end that.

“It’s really unfortunate that Duke Energy is allowed to continue protecting its monopoly against competition and to keep stifling the growth of cheaper, clean solar power,” Warren said in an interview. “Duke Energy’s business policy is to continue doing the bare minimum” and expand use of fracked natural gas, he added. Duke Energy is helping build a natural gas pipeline through eastern North Carolina.

Duke Energy Progress, an operating subsidiary serving eastern North Carolina, ranked fourth among electric utilities nationally in adding solar power and storage units in 2017, according to the Smart Electric Power Alliance.

The commission ordered NC WARN to refund its charges to Faith Community Church and pay a $200 fine for each day of electric service, but the panel said the penalties would be waived in part if they stayed out of the utility business. Warren said his group expected the penalties of nearly $60,000 would be set aside.