Sen. Amy Klobuchar Amy KlobucharSocial media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE (D-Minn.), a 2020 presidential candidate, is proposing changes to Environmental Protection Agency (EPA) biofuel regulations that could help her win over support in Iowa.

Speaking at a campaign stop over the weekend in Iowa, the country's top corn producer, Klobuchar called for the EPA to give away fewer of its waivers that allow oil refineries to avoid mixing their fuel with ethanol, according to Reuters.

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The waivers, aimed at helping small refineries meet fuel standards, exempt some refineries from the Renewable Fuel Standard (RFS), which requires oil refiners to blend ethanol with their gasoline pool or purchase credits from refiners that do.

Smaller refineries with a capacity of less than 75,000 barrels per day can obtain a waiver after proving that complying with the rule could cause financial stress. But ethanol groups and politicians representing corn-producing states have long called for the EPA to reconsider how it grants the waivers.

Klobuchar called the EPA’s waivers “misguided” and said the biofuels trading market is manipulated by financial institutions, according to Reuters.

She called for new compliance standards and oversight, a stance likely to drum up support from ethanol groups and leaders in Iowa, a key battleground state in the 2020 race.

Ethanol makers have long argued that too many companies qualify for waivers and that the process is not transparent. While the Trump administration has voiced support for the ethanol industry’s plea to extend the use of gas mixed with 15 percent ethanol year-round, it has also made extensive use of small refinery waivers. Even major companies like Exxon Mobil Corp received exemptions for certain facilities.