– The Trump administration said Friday that it has lifted a summertime ban on the use of E15, a gasoline blend made of 15% ethanol. The move is designed to help corn and soybean farmers harmed by President Donald Trump's decision to impose tariffs.

Ethanol, made from corn and other crops, has been mixed into some types of gasoline for years as a way to reduce reliance on oil, among other things. However, burning ethanol-blended fuel in the summertime heat has a side effect of increasing smog — and for that reason the lifting of the ban raised objections from environmentalists. Oil companies also criticized the end of the summertime ban because a wider use of ethanol will cut into their sales of gasoline.

Nevertheless, the change has the potential to reap political benefits for Trump as he gives the agriculture industry a policy change it has long sought. The formal lifting of the ban follows through on a promise Trump made to farmers on a trip to Iowa last fall, as he sought to shore up support for Republicans in the Midwest. The ban has been in place since 2011 and Trump has criticized it as "ridiculous."

"I appreciate President Trump's steadfast support for our patriotic farmers and for his commitment to expand the sale of E15 and unleash the full potential of American innovation and ingenuity as we continue to demonstrate our rightful place as the world's leader in agricultural and energy production," Agriculture Secretary Sonny Perdue said in a statement.

The summertime ban "made it very difficult to market E15," said William Wehrum, head of the Clean Air Office at the Environmental Protection Agency, which administers the ethanol regulations. "We think this will result in increasing the amount of ethanol blended into gasoline."

Oil refiners are required to blend some ethanol into gasoline under a pair of laws, passed in 2005 and 2007, intended to lower the use of oil and greenhouse gas pollution by mandating increased levels of ethanol in the nation's fuel mix every year. However, since passage of the 2007 law, the mandate has been met with criticism that it has contributed to increased fuel prices and has done little to lower greenhouse gas pollution.

Farm groups cheer move

"Removing outdated barriers and regulations is a commitment that this administration continues to make good on," said Zippy Duvall, president of the American Farm Bureau Federation. "After years of declining farm income, opening up markets to additional fuel choices for consumers helps create new demand that farmers desperately need."

The oil industry and environmental groups criticized the move.

"Extending this waiver is an anti-consumer policy that risks causing costly engine and fuel-system damage to nearly three out of four vehicles on the road today," said Frank Macchiarola, a vice president of the American Petroleum Institute, which lobbies for oil companies. "This premature policy attempts to push E15 into the market before it is ready."

Collin O'Mara, president of the National Wildlife Federation, said: "Allowing the year-round sale of E15 gasoline is both illegal under the Clean Air Act and will accelerate the destruction of wildlife habitat and pollution of our air and drinking water."

Oil industry foes are preparing to go to court to fight the EPA regulation issued Friday.

The agency's final rule offers ethanol producers and corn farmers the promise of greater market access and demand — but the coming legal battle will be the true test of that potential.

Ethanol is already a staple of America's fuel supply, accounting for about 10% of total consumption. Biofuel boosters who have lobbied for the regulatory shift are betting 15% will eventually emerge as the standard. Green Plains Inc. CEO Todd Becker said this month that the higher blend puts in play "year-round demand growth of at least 200 million gallons of annualized incremental demand as only the starting point."

That would come at the expense of the oil industry. "This action by EPA makes no sense and is contrary to the law, congressional intent and decades of agency precedence," said Macchiarola. "We will challenge it ­vigorously."

The American Petroleum Institute previewed its legal argument in public comments, arguing that the agency is flouting the plain text of the Clean Air Act by extending an existing waiver to E15. Marathon Petroleum Corp. warned the EPA's move to consider E15 "substantially similar" to conventional E10 gasoline is "arbitrary and capricious" — a fatal failing under a federal law governing rule-making. And the American Fuel and Petrochemical Manufacturers insisted the EPA is taking action previously rejected by Congress.

Ethanol advocates argue that the EPA is on solid legal footing. The agency's move to grant a waiver to E15 "reflects the best, most natural reading" of the Clean Air Act, and that higher-ethanol blend is substantially similar to E10, said Growth Energy Chief Executive Officer Emily Skor.

Bloomberg News contributed to this report.