In a letter to Shaun Donovan, director of the Office of Management and Budget, Branstad and Gov. Pat Quinn, D-Ill., said the proposed reduction to the renewable fuel standard would be especially damaging to biodiesel and cellulosic ethanol, the fledgling industry where the fuel is made from crop residue, grasses and wood chips and other plant materials. The OMB is in charge of vetting proposed regulations.

Last November, the Environmental Protection Agency, which oversees the RFS, proposed sharply cutting ethanol made from corn and cellulosic materials in 2014, while leaving the biodiesel level at the same amount as the prior year. The EPA has not issued the final blending requirements for 2014, but an announcement is expected this fall.

“The adoption of EPA’s proposed 2014 RFS volume requirements threatens to have a negative economic impact on the rural economy and on the biofuels industry, specifically on biodiesel and cellulosic ethanol,” Branstad and Quinn, both members of the Governors’ Biofuels Coalition, said in the Wednesday letter.

The governors said the proposed cuts already have curtailed investments in biodiesel and cellulosic, which has hurt rural economies that depend on renewable fuels.

Iowa is the nation’s leader in renewable fuels production. It has 42 ethanol refineries capable of producing more than 3.8 billion gallons annually and 12 biodiesel facilities with the capacity to produce almost 315 million gallons annually.

Last month, Branstad, an ardent biofuels supporter, charged EPA Administrator Gina McCarthy with being misleading in her support for renewable fuels.