California air quality regulators on Friday tightened a key environmental program credited with reducing the amount of pollution churned out by cars and trucks but criticized for raising the state’s already high gasoline prices.

Regulators say the changes are essential to reducing carbon emissions. But political leaders in both parties are worried that gas prices could further increase.

Experts don’t know how much gas prices may rise from the revised California climate program, which tightens standards and gives incentives for low-carbon fuels. The board ordered an annual review of the cost impacts.

California regulators have approved plans to strengthen the state’s carbon reduction standards — a move that opponents fear could drive up gasoline prices. The decision, which occurred following a 12-hour meeting Friday,

Gas prices could soon rise as California aims to reach carbon emission goals in a state already dealing with some of the country's highest costs at the pump.