By Dec. 1, the Environmental Protection Agency must decide whether to approve a request to increase the amount of ethanol that can be mixed with most gasoline sold at pumps to as much as 15 percent.
Most pumps already sell E10, which is 10 percent ethanol.
Automakers want the agency to further study the effects of the proposed increase before allowing it to happen.
Increased ethanol blends could corrode engines that aren't specifically built for E15, according to automakers.
Four farm state senators led by Ben Nelson, D-Neb., introduced a measure that would require the EPA to grant the request.
More than 13,000 people and groups have written the EPA since the request was filed in March.
Congress has required that the nation use 11 billion gallons of ethanol next year and 36 billion gallons by 2022.
Mike Stanton, CEO of the Association of International Automobile Manufacturers, the trade group representing major foreign automakers, noted the United States would not be able to consume even half of the ethanol required by Congress by 2022 by simply requiring all pumps to be E10.
"We're on a collision course here," he said.
And there are a number of problems with an immediate boost in the ethanol blend.
Automakers warn the higher ethanol blend could boost greenhouse gas emissions, damage engines or disable vehicles.
In Baltimore, nearly a third of the city's patrol cars stopped running earlier this month because a station had boosted the amount of ethanol in the fuel. It isn't clear how much ethanol was in the mix. More at Detroit News