FILE PHOTO: U.S. Environmental Protection Agency (EPA) Acting Administrator Andrew Wheeler addresses staff at EPA headquarters in Washington, U.S., July 11, 2018. REUTERS/Ting Shen/File Photo

WASHINGTON (Reuters) - A U.S. Environmental Protection Agency rule to allow sales of higher-ethanol blends of gasoline year-round is being delayed by a partial government shutdown, acting Administrator Andrew Wheeler said on Wednesday.

The rule, a key campaign promise by President Donald Trump to farmers, an important constituency, was announced in October and would aim to expand the market for corn-based ethanol.

Speaking at his Senate confirmation hearing, Wheeler, Trump’s nominee to head the agency on a permanent basis, said the EPA was unable to work on the rule at the moment because of the shutdown.

“Originally we were planning on issuing the rule in February ... We haven’t been shut down as long as the other departments but we may be slightly delayed at this point,” Wheeler said.

A partial government shutdown began on Dec. 22 due to Trump’s insistence on more than $5 billion to pay for a wall along the U.S. border with Mexico. Currently there is little sign of a breakthrough.

Wheeler said the rule would still be ready for the 2019 driving season which begins in June. Following the official release of the proposed rule, the EPA will be required to get public comment.

Known as E15, the rule could be politically helpful to Republican candidates in the Midwest, which is saddled with a tough farm economy and suffering from the U.S.-China tariff-laden trade war.

Last October, Trump deliver a long-sought political victory to the Farm Belt but angered oil refiners. He announced the lifting of a ban on summer sales of gasoline blended with 15 percent ethanol.