(Reuters) - A group of senators from U.S. corn states have asked President Donald Trump for a meeting about the nation’s biofuels law, amid expectations the administration will soon act to lower the regulation’s costs to the oil refining industry.

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The group of Republican senators wrote a letter to Trump on Thursday in which they opposed a plan he is considering to limit the price of credits that oil refiners must acquire to comply with the Renewable Fuel Standard.

“Let there be no doubt - the consequences of a waiver would be severe and immediate across the Midwest, impacting farmers and biofuel stakeholders alike,” the senators wrote.

The letter was written by Senators Chuck Grassley and Joni Ernst, of Iowa; John Thune, of South Dakota; Roy Blunt of Missouri; and Deb Fischer of Nebraska.

Trump has not publicly commented on his plans. But he told lawmakers and industry officials in a closed-door meeting earlier this month that he supported capping the price of RFS compliance credits, known as RINs, at 10 cents each, according to a source who attended but who asked not to be named.

The credits are currently trading around 42 cents each, having fallen nearly 40 percent in recent weeks amid the political uncertainty.

White House spokeswoman, Kelly Love, did not respond to a request for comment.

In the closed-door meeting this month, Trump also supported expanding sales of high-ethanol gasoline – a tweak long-sought by ethanol producers, according to the source.

The Environmental Protection Agency bans the use of gasoline containing 15 percent ethanol during the summer months, a measure intended to reduce ozone emissions and smog during the peak driving season.

The corn-state senators, along with the biofuel industry, like the idea of lifting the summer ban on 15-percent ethanol blends, but oppose any credit price caps. They argue the proposed caps would take away any incentive to blend higher volumes of ethanol.

Grassley took to Twitter on Thursday night and Friday morning to oppose the RIN caps.

“@realDonaldTrump I want to shake up what u might be planning abt RINs cap for a short period. It will be CATASTROPHIC to ethanol,” Grassley wrote.