(Adds comment from senators and context)
NEW YORK, April 9 (Reuters) - Five Republican senators on Monday called on President Donald Trump to temporarily halt the use of biofuels policy waivers for small oil refineries, after reports the Environmental Protection Agency had issued a recent wave of such exemptions.
The group of lawmakers, which includes Senators Charles Grassley and Joni Ernst of Iowa and John Thune of South Dakota, said the EPA waivers are "undermining" the U.S. Renewable Fuel Standard, a law that requires biofuels like ethanol to be added to the nation's fuel, which Trump has said he supports.
"We therefore urge you to call on the EPA to cease all RFS waiver action until the agency's administration of the RFS can proceed in a more transparent and impartial manner," the senators said in a letter dated April 9.
The request comes as Trump is scheduled to meet with EPA head Scott Pruitt and Secretary of Agriculture Sonny Perdue on the issue later on Monday.
An EPA source told Reuters last week that the agency had issued 25 small refinery exemptions, relieving the plants of their requirements to blend biofuels last year.
Reuters also reported that Andeavor, one of the country's largest refiners, also received EPA exemptions from the biofuels law for three of its smallest refineries.
In the past, the EPA has issued between six and eight waivers from the RFS per year to small refining operations of less than 75,000 barrels per day that can demonstrate they are struggling financially to comply, according to a former official familiar with the waiver program under past administrations.
But refiners have applied for the waivers in larger numbers after a federal appeals court ruling last year that said the EPA must expand the guidelines for approving them.
They have also been encouraged to apply by the Trump administration's recent efforts to broker a deal between the oil and corn industries to reduce the costs of the RFS, industry sources said. Those talks have not yielded a deal.
"The EPA is using its small refinery waiver in an unprecedented manner to benefit some of the largest refineries in the nation, including Andeavor, which posted profits of approximately $1.5 billion last year," the senators wrote.
White House spokeswoman Kelly Love did not immediately respond to a request for comment.
The RFS requires refiners to blend biofuels, or purchase blending credits from other companies - a policy intended to help farmers, and cut pollution and fuel imports. (Reporting by Jarrett Renshaw; writing by Chris Prentice; editing by Jonathan Oatis and Chizu Nomiyama)