(Bloomberg) -- Darling Ingredients Inc., a major US producer of renewable diesel, defended imports of used cooking oil as a feedstock to produce climate-friendly fuels.

The US has been flooded with used cooking oil — or UCO — from China, eroding profits for companies that crush soybeans to make renewable diesel and sustainable aviation fuel. The increase has stirred speculation that some imports may not be authentic and instead are mixed with fresh vegetable oils, potentially undermining US biofuel laws. A US soybean trade group is calling for increased tariffs on Chinese UCO. 

Chinese imports are “a legitimate source of used cooking oil,” Darling Chief Executive Officer Randall Stuewe said, noting that there are 12.6 million restaurants in China and only 700,000 in the US.

“That doesn’t mean there aren’t some bad actors out there, but at the end of the day there are legitimate suppliers,” Stuewe said at the BMO Global Farm to Market conference in New York.

Read More: Suspicions of Fake China Cooking Oil Alarm US Biofuel Industry

Darling, a food ingredient seller, produces renewable diesel through its Diamond Green Diesel partnership with Valero Energy Corp. Stuewe said the company hasn’t come out against UCO imports because the company operates on many fronts, including importing used cooking oil.  

“The reality is that it is all legitimate and it is the lowest carbon intensity feedstock in the world,” he said.

The CEO also said he sees robust demand for sustainable aviation fuel. “Ultimately, the margins are coming back into where we thought they would and ultimately, we’re oversubscribed,” Stuewe said. He added that Diamond Green’s first SAF plant under construction in Port Arthur, Texas, is close to being completed.

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