The U.S. Supreme Court on Monday declined to hear a high-profile challenge to Washington’s Climate Commitment Act, marking yet another victory for the state’s keystone climate policy.

The lawsuit started with the private operator of a natural gas power plant in Grays Harbor County. The plant is required to buy pollution allowances to pay for the many tons of greenhouse gasses it emits into the atmosphere under the 2021 Cap and Invest” law.

The plant’s owner, Chicago-based Invenergy, sued Laura Watson, then-head of Washington’s Department of Ecology, in late 2022, arguing that the state’s carbon market is unconstitutional. The lawsuit claimed that the state law discriminated against privately operated natural gas plants (public utilities receive allowances free) and unfairly treated it as

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