washington eight democratic senators ask u.s. regulators tuesday launch investigation billionaire carl icahn activities u.s. biofuels blend credit market say activist investor may violate trade laws since become adviser president donald trump write request agencies investigate whether carl icahn violate insider trade laws anti-market manipulation laws relevant laws base recent action market renewable fuel credit senators say letter head securities exchange commission commodity futures trade commission environmental protection agency letter copy see reuters sign elizabeth warren massachusetts sheldon whitehouse rhode island sherrod brown ohio five others agencies require act efforts reach icahn comment immediately successful months public outcry democratic lawmakers liberal watchdog group concern icahn dual role high-powered investor presidential adviser could lead conflict interest trump republican name icahn unpaid adviser regulation shortly november election say choice could help slash red tape bolster economic growth february icahn submit proposal white house change u.s. biofuels program way would ease regulatory burden oil refine company already struggle low profit margins icahn own majority stake refine company cvr energy inc cvi.n white house consider proposal administration official immediately respond request comment tuesday reuters review securities file last month show cvr accumulate large short position biofuels blend credit call renewable identification number rins many refiners require purchase biofuels law mean company would strong position profit rin price fell letter senators point rin price drop sharply late february icahn proposal biofuels regulation report way know time whether mr. icahn make renewable fuel credit trade decisions trade base material non-public information otherwise manipulate market senators write publicly available evidence trouble base evidence ask agencies investigate whether mr. icahn conduct violate laws jurisdiction say icahn previously dismiss accusations proposal white house change biofuels program self-serving say overhaul would help refine company include competitors cvr energy share fell 0.4 percent 22.20 tuesday cvr spokesman decline comment share icahn investment firm icahn enterprises iep.o fell 4.3 percent 50.82 icahn 81 spend decades battle major company activist investor amass fortune forbes magazine peg 20 billion recent years build 82 percent stake cvr make player niche biofuels market carl icahn shy know voice action special adviser influence rin market say tyson slocum public citizen liberal watchdog group already ask congress investigate whether icahn violate lobby disclosure laws real issue carl icahn use position special adviser unduly impact rin market make correspond bet move slocum say cvr energy refine unit cvrr.n post net gain 6.4 million associate biofuel credit market first quarter 2017 50 million turnaround year-ago period cvr shell 43.1 million company say file u.s. renewable fuel standard oversee u.s. environmental protection agency require increase volumes biofuels blend nation gasoline diesel every year place responsibility mainly refiners require blend fuel purchase credit others icahn proposal call regulators shift responsibility blend refiners many lack sufficient blend capacity terminal operators number biofuels group oppose propose change say could undermine renewable fuel standard make complicate since many time terminal operators refine company move point obligation would require dramatic increase staff require track epa deliver poor supervision increase complexity program ultimately high cost american drivers say growth energy chief executive emily skor u.s. democratic senators seek probe icahn biofuel credit deal