Eight Democratic Senators have demanded a probe into billionaire investor and President Trump adviser Carl Icahn's activities in the U.S. biofuel market, focusing on possible insider trading. 

"We are writing to request that your agencies investigate whether Carl Icahn violated insider trading laws, anti-market manipulation laws, or any other relevant laws based on his recent actions in the market for renewable fuel credits," the Senators said in a letter to the heads of the Securities and Exchange Commission Tuesday. 

Icahn proposed changes to the U.S. biofuels program that would ease the regulatory burdens of biofuel companies in February, shortly after he was named an adviser to Trump's administration following his election in November. 

Icahn holds a majority stake in CVR Energy  (CVI - Get Report) .

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