(AP) — An association representing oil refineries launched a television ad in four swing states Monday criticizing President Donald Trump’s moves to expand the use of ethanol in gasoline.

The American Fuel and Petrochemical Manufacturers’ 30-second spot will run statewide through July in Michigan, Pennsylvania, Ohio and Wisconsin. The group didn’t immediately say how much it was spending on the buy.

The ad claims that Trump promised a “win-win energy policy for all Americans. But for small refineries, unchecked ethanol mandates are job killers, hurting the backbone of our manufacturing economy.”

It goes on to say: “President Trump, only you can fix this.”

The ad underscores how Trump’s administration has found itself caught between the oil industry and corn growers, two key flanks of Trump’s base.

For more than a decade federal law has mandated that oil refineries mix ethanol into their fuel. The Trump administration’s former Environmental Protection Agency chief, Scott Pruitt, had angered lawmakers, growers and ethanol processors by granting exemptions sparing refineries from that mandate. The dispute sparked a billboard campaign and a tractor rally by angry Midwestern farmers last year.

This past May the administration tried to calm the dispute by lifting a summertime ban on gasoline mixed with 15% ethanol . The ban had been imposed out of smog concerns but the administration’s move cleared the way for year-round sales and expanded the ethanol market. Only a fraction of U.S. gas stations currently sell the 15% blend, known as E15.

Officials in the EPA Region 5 office, which is responsible for Wisconsin, Michigan and Ohio, didn’t immediately respond to an email Monday seeking comment on the ad. No one immediately responded to an email sent to the general inbox for the EPA Region 3 office, which oversees Pennsylvania.

Jim Zook, executive director of the Michigan Corn Growers Association, said the ethanol industry has created hundreds of jobs and contributed to millions of dollars of economic activity.

“This ad is nothing more than another attempt by the petroleum industry to maintain their near-monopoly on the fuel supply at the expense of American consumers,” Zook said.

No one immediately responded to emails sent to corn grower associations in Pennsylvania, Ohio and Wisconsin.