By Chris Prentice, Reuters.

(Reuters) - U.S. biofuels regulations, which mandate mixing corn-based ethanol into gasoline, have lately drawn together a diverse cast of political opponents.

They include an upstart gas station owners' trade group, a former Obama administration environmental adviser and billionaire activist investor Carl Icahn, who owns a refiner and served as U.S. President Donald Trump's special advisor on business regulation - until he resigned Friday amid allegations of a conflict of interest.

Even the Renewable Fuels Association (RFA), a leading biofuels industry group, recently dropped its opposition to policy changes sought by this ad hoc coalition.

These players would seem to have few shared interests, but they share one key connection – close ties to Valero Energy Corp. (VLO.N), America's largest oil refiner.

As part of an extensive behind-the-scenes lobbying campaign, Valero played a key role in bringing these people and groups together around a policy proposal that could save the refiner hundreds of millions of dollars each year in regulatory costs, according to two former Valero executives with knowledge of the firms' lobbying strategy.