The Washington State Supreme Court has ruled that the state’s natural gas initiative is unconstitutional.

Voters passed Initiative 2066 with about 52% of the vote in November 2024, but it was struck down in Superior Court earlier this year. Not long after, state Attorney General Nick Brown and the Building Industry Association of Washington asked the state’s Supreme Court to weigh in.

The Republican-led initiative was spearheaded by the building association and was supported by the Washington Hospitality Association and political action committee Let’s Go Washington.

Across the country, laws around natural gas use have emerged as a highly contentious issue, and in recent years, several states and municipalities have passed rules prohibiting local bans on natural gas.

The initiative sought to explicitly protect access to natural gas in Washington and weaken building codes that make it more difficult and costly to include natural gas heating in new construction. It also targeted legislation intended to help Puget Sound Energy, the state’s largest utility, plan its transition away from natural gas.

For nearly two years, the initiative injected uncertainty in parts of the state including utility regulators, builders and municipal programs incentivizing building electrification and energy efficiency.

In March 2025, King County Superior Court Judge Sandra Widlan ruled that the initiative was unconstitutionally broad, violated the state’s single-subject rule and improperly changed existing laws.

The Washington state Supreme Court affirmed the ruling, except on narrower grounds. It says the initiative violated only the state’s single-subject rule, which is intended to protect against “logrolling,” or when a law combines several different proposals to garner support — although a voter may not individually approve of all changes.

Six justices signed the majority opinion, striking the initiative down, and three dissented, led by Justice Sal Mungia.

The plaintiffs challenging the initiative included advocacy groups Climate Solutions, Washington Conservation Action and Front and Centered, plus King County, the city of Seattle and other parties.

Sierra Club Deputy Director Dylan Plummer also called the ruling a “clear refutation of this cynical tactic by the fossil fuel industry” to rollback climate policies with a “misleading initiative.”

According to a press release sent out by the group, the ruling brings certainty to several energy efficiency and decarbonization measures and allows changes like the state’s building code council’s updates to go forward. The building code changes incentivizing all-electric construction had been previously challenged by the building association.

Those in support of the initiative expressed their “deep disappointment” with the court’s ruling, arguing it subverts the will of the people who voted for the initiative, according to news release from the building association.

The Washington Hospitality Association vowed to continue advocating for “energy policy that gives our members realistic timelines and real choices …”

In a statement, Let’s Go Washington founder Brian Heywood said the decision “appears to be a coordinated effort by all three branches of the government to annihilate the initiative process itself,” and accused the state Supreme Court of consistently applying their “judicial thumb in favor of the government” over the people.