US biodiesel producers fear the recent scandal uncovering phony renewable fuel credits could erode support for the federal energy policy at a crucial time in its implementation.

National Biodiesel Board CEO Joe Jobe on Monday urged opponents of the Renewable Fuel Standard to avoid the temptation to use the fake credits as a weapon to bludgeon the mandate, which requires an increasing share of biofuels get blended into the US transportation fuel supply.

"Opponents of the RFS will use any flaw to characterize it as a failed program," Jobe told the group's annual conference in Orlando. "But it's not a failed program. It's working, and we have to make it work better."

Federal investigators and the Environmental Protection Agency's compliance division have flagged two sellers of renewable identification numbers (RINs), codes that should correspond with actual biofuel production to satisfy renewable energy mandates. In November, EPA declared invalid 32.3 million biodiesel credits sold by Clean Green Fuels of Maryland. Last week, the agency tossed out 48.1 million biodiesel credits sold by Absolute Fuels of Texas.

More violation notices could be coming from EPA, predicted Jobe and Charlie Drevna, president of the American Fuel and Petrochemical Manufacturers Association, the top lobby for US refiners.

Drevna said the "debacle" unfairly penalizes members of his group for buying RINs in good faith without being able to verify whether sellers produced the fuels that the credits purported to represent.

"We're forced to buy these things, and these folks are supposedly registered by the EPA," he told Jobe during the same conference. "We go out and do it. They're frauds. We get to buy them again, we get fined and the EPA says, 'Caveat emptor.'"

Drevna said refineries' lawyers have to huddle to fight the violation notices. Last week's notice went to the RIN producer, while the November notice went to 24 "obligated parties," or those refiners and renewable fuel exporters that bought the credits to comply with the federal mandate.

While Jobe said he commended EPA for taking RIN fraud seriously and cracking down on it, Drevna told the agency's representatives at the conference: "You guys screwed this one up."

Jobe asked Drevna and other RFS opponents to demonstrate the same restraint that the biodiesel industry showed after BP's Macondo disaster.

"We didn't use that to disparage the petroleum industry, because all of our members have customers and contracts and partnerships with the petroleum industry," Jobe said. "It is our policy not to badmouth your customers. We've worked every hard at that. We hope that was noticed. We hope we'll get some points for that."

Drevna said neither he nor the refiners group would attack biodiesel producers "because of a couple of yo-yos."

"This is more than an anomaly, this is way off the charts," he added.

Nevertheless, Drevna promised to keep fighting to end the RFS program, which he said contributed to Northeast refinery closures and would eventually eliminate 22% of the industry's market. He called the program an anachronism adopted when the US was considered energy poor, before oil and natural gas producers ratcheted up deepwater and shale production.

"Should biodiesel be part of the mix? Abso-positively. No question," Drevna said. "Should there be a mandate? If it's a good product, which it is, if it can compete, which it does, so be it. But we as the industry can't just focus on your particular bucket as we call it."

Jobe defended the RFS program and urged members to do the same in Washington.

"The petroleum sector has a 100-year head start on us," he said.