SEATTLE — A groundbreaking law that forces companies in Washington state to reduce their carbon emissions while raising billions of dollars for climate programs could be repealed by voters this fall, less than two years after it took effect.

The Climate Commitment Act, one of the most progressive climate policies ever passed by a state legislature, is under fire from conservatives, who say it has ramped up energy and gas costs in Washington, which has long had some of the highest gas prices in the nation. The law aims to slash emissions to almost half of 1990 levels by the year 2030.

It requires businesses producing at least 27,600 tons of carbon dioxide, or the equivalent in other greenhouse gases, including methane, to pay for the right to do so by buying “allowances.” One allowance equals 1.1 tons of greenhouse gas pollution, and each year the number of allowances available for purchase drops, theoretically forcing companies to find ways to cut emissions.

Supporters of the policy say not only would a repeal not guarantee lower costs, but billions of dollars in state revenue for years to come are at stake. Many programs already are or will soon be funded by money from polluting companies, including projects on air quality, fish habitat, wildfire prevention and clean energy.

“The grand policy goal is the higher-level thing of fighting climate change, reducing carbon emission,” said Todd Donovan, a professor of political science at Western Washington University. “But you get down below 30,000 feet to the voters and it’s, ‘How does this effect my gas taxes?’ ”

The group behind the repeal effort, Let’s Go Washington, says the carbon pricing program has increased consumer gasoline costs by 43 to 53 cents per gallon, citing the conservative think tank Washington Policy Center.

For months, Let’s Go Washington, which is primarily bankrolled by hedge fund executive Brian Heywood, has held more than a dozen events at fuel stations to speak out against what it calls the “hidden gas tax.” Last month at a station in Vancouver, in southwestern Washington, the group lowered gas prices by $1 for two hours by subsidizing the difference to show what reduced prices would look like.

“It’s making everything more expensive, because everything you buy gets delivered to the store or to your door on a truck,” Let’s Go Washington spokesperson Hallie Balch said in a video about the initiative last month.

The average price at the pump for regular gas has gone as high as $5.13 per gallon since the auctions started in February 2023, though it has since fallen and stood at $4.05 this month, according to GasBuddy.

Supporters of keeping carbon pricing have showcased the many programs it finances and could disappear if the repeal succeeds, including ones to help Native American tribes respond to climate change.

“We know that the only guarantee of Initiative 2117 is that it would cut investments in combating pollution and air quality, in fish habitat, in preventing wildfires and in transportation,” said Mark Prentice, spokesperson for No on 2117, the group in favor of keeping the climate policy.

Without the program, the Office of Financial Management estimates, $758 million would be lost in state revenue in the next fiscal year and $3.1 billion over the following four years. During this year’s legislative session, state lawmakers approved a budget through fiscal year 2025 with dozens of programs funded by carbon pricing revenue, with belated start dates and stipulations that would not take effect if that disappears.

Washington launched the program after California’s initiative. It started out with emissions targets of 7% annual decreases, set to ease up from 2031 on. Repealing it would sink plans to link up Washington’s carbon market with others and could be a blow to its efforts to help other states launch similar programs.