WASHINGTON (AP) – The Environmental Protection Agency has approved blending higher concentrations of ethanol into gasoline for newer vehicles, allowing the corn-based fuel to be up to 15 percent of mixtures sold at the pump.

The current maximum blend is 10 percent. The EPA announced Wednesday that the higher blend will be approved for cars and light duty trucks manufactured since 2007, if retailers want to sell it.

The move, which comes less than a month before November’s midterm elections, is politically popular in rural farm areas. But ethanol faces strong opposition from the auto industry, environmentalists, cattle ranchers, food companies and a broad coalition of other groups.

Opponents argue that the increase in production of corn and its diversion into ethanol is making animal feed more expensive, raising prices at the grocery store and tearing up the land. Manufacturers of smaller engines – used in everything from lawn mowers to boats – also oppose increasing the use of the fuel, saying those engines are not designed for the higher concentrations.

The Obama administration has remained supportive of the renewable fuel, and the EPA has said a congressional mandate for increased ethanol use can’t be achieved without allowing higher blends. Congress has required refiners to blend 36 billion gallons of biofuels, mostly ethanol, into auto fuel by 2022.

The ethanol industry has maintained that there is sufficient evidence to show that a 15 percent ethanol blend in motor fuel will not harm engine performance. They say increased consumption of the renewable fuel creates new jobs and replaces imported oil.

The industry group Growth Energy petitioned the EPA to raise the blend in March. The decision was initially expected in December but was delayed twice as the agency and the Energy Department completed additional testing. The EPA is expected to make a second decision on the ethanol concentration allowed in cars manufactured between 2001 and 2006 after more testing is completed at the end of November.

The agency said there will not be a decision this year on ethanol changes for cars and light trucks manufactured before 2001 – or for any motorcycles, heavy-duty vehicles, or non-road engines – because there is not sufficient testing to support such an approval.

The decision could cause confusion at service stations as people would have to consider which pump to use based on the age of their car. The EPA said it will also propose new pump labeling requirements to help consumers figure out which gas to use.

Critics said the decision could be a frustration to drivers.

“We’re really going to make the consumers a guinea pig here,” said Craig Cox of the Environmental Working Group, an environmental advocacy group that opposes increases in the fuel. “Have we really thought through what it’s going to take to distinguish E15 to E10?”

The Obama administration’s decision to boost the ethanol concentration in gasoline is a victory for the industry as it struggles to hold on to other subsidies. An increased public skepticism of the renewable fuel has caused some lawmakers who have always championed ethanol to divert the money to other priorities. A key tax credit is scheduled to expire at the end of this year, and some in Congress are considering cutting it or doing away with it altogether.

Ethanol producers say expiration of the credits, which are paid to oil companies as an incentive to blend gasoline with ethanol, could mean the loss of almost 40 percent of the industry’s plants and tougher times for a domestic fuel that is good for national security.

Critics say the industry should stand on its own after receiving subsidies for 30 years and argue the tax credits are a waste of taxpayer dollars.