Gas prices in California are forecast to surge by 50 cents (40p) per gallon due to a new emissions reduction programme.
The California Air Resources Board Low Carbon Fuel Standard 2023 amendments impact assessment suggested that drivers would feel the squeeze over the next two years.
Prices are estimated to jump by 47 cents per gallon in 2025 and 52 cents in 2026 - excluding the existing gas tax in the state.
On Monday, the average cost per gallon in California was $5.286 (£4.21), compared to a national average of $3.619 (£2.88).
The Democrat state currently enforces a gas tax of $0.58 (£0.46) per gallon - the highest in the country.
The Low Carbon Fuel Standard was launched in 2007 by former Gov Arnold Schwarzenegger to reduce the state's carbon emissions.
Republicans in California are urging Governor Gavin Newsom to suspend the state's gas tax as prices continue to surge.
"No one knows about this. I think people just think it's a tax, so they don't know the difference between the carbon tax versus the state tax," California state Senator Janet Nguyen told Fox News Digital.
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"It's almost like a tax on the tax. The middle class, the low income, they can't afford gas to go to school, work or grocery or the doctor's office."
The California Air Resources Board is said to be amending its programme to align with a plan to hit carbon neutrality by 2045.
The board postponed a March vote on the proposal.
Newsom said oil companies profiteering is to blame for the enormous additional cost on California's drivers.
In April, gas prices topped $7.29 (£5.80) per gallon in some parts of California.
The rate was above the current national hourly minimum wage.
Motorists in a Silicon Valley town are facing particularly high rates which set them back almost $150 (£119) for a full tank.
