NEW YORK, July 20 (Reuters) - A bipartisan group of U.S. senators introduced legislation on Tuesday that would eliminate a national mandate requiring oil refiners to blend corn-based ethanol into their fuel mix - a proposal that would slam corn growers and is likely to face vehement opposition from the farm lobby.

Republican Senator Pat Toomey from Pennsylvania and Democratic Senator Bob Menendez from New Jersey, part of the group introducing the bill, represent states with oil refineries that claim the mandates are expensive and threaten refinery jobs.

Lawmakers from both states have been pushing the Biden administration to relieve refineries of their obligations under the U.S. Renewable Fuel Standard, which was enacted to expand the market for U.S. renewable fuels and boost energy independence.

Democratic Senator Dianne Feinstein from California and Republican Senator Susan Collins from Maine joined Toomey and Menendez in introducing the bill. They say that other biofuels have lower greenhouse gas emissions, though ethanol proponents argue the product is a good option to help fight climate change now.

The senators claim the bill would help reduce carbon emissions from transportation fuels by removing volume requirements for corn ethanol, while leaving in place obligations for other biofuels and biodiesel.

Under the RFS, refiners must blend some 15 billion gallons of ethanol into their fuel each year - a huge boost to the corn industry - along with billions of gallons of other types of biofuels.

"The federal corn ethanol mandate no longer makes sense when better, lower-carbon alternatives exist," Feinstein said in a statement. "It's time to end the mandate and instead support more advanced biofuels and biodiesel that won't contribute to climate change or drive up the cost of food.”

Ethanol's effect on carbon dioxide emissions depends on how it is made and whether indirect impacts on land use are calculated, according to the U.S. Energy Information Administration.

The Advanced Biofuels Business Council spoke out against the bill on Tuesday.

"This proposal does nothing for advanced biofuels and we do not appreciate being used to greenwash a top priority for a handful of the dirtiest oil refineries in the country," said Brooke Coleman, the council's executive director.