Five Republican senators, led by Sen. Ted Cruz (R-Texas), pose a threat to the confirmation of Andrew Wheeler, President Donald Trump’s nominee to replace Scott Pruitt as EPA administrator, Bloomberg’s Jennifer A. Dlouhy and Mario Parker reported Feb. 13.

The issue is concerns the senators have over biofuels and whether Wheeler, who currently serves as acting administrator, “will take steps to help oil refiners forced to blend biofuel into gasoline.”

“Without an adequate proposal to meaningfully lower the regulatory burden, we will have serious concerns with your nomination,” the senators said in a letter, which was dated Feb. 11 and obtained by Bloomberg.

Cruz, Pat Toomey (R-Pa.), Mike Lee (R-Utah), John Kennedy (R-La.) and Bill Cassidy (R-La.) all signed the letter, which Bloomberg says “laid out a raft of concerns with the Renewable Fuel Standard that mandates biofuel use, a top target for oil refiners in their home states.”

“As we continue to evaluate your nomination to be administrator, it is important that we have a better understanding of your views and approach to administering the RFS and the agency actions you believe could alleviate costs,” Bloomberg quoted the letter.

Wheeler allowed year-round sales of E15 gasoline in January prompting immediate concerns from lawmakers in oil-producing states.

This time, senators with home-state oil interests have asked Wheeler if the EPA will alter biofuel blending targets as part of a broad upcoming “reset” of the RFS program. They also asked Wheeler to agree that under a recent court ruling, the EPA isn’t required to redistribute waived biofuel quotas to non-exempted refineries. Oil industry leaders have argued against any such reallocation, arguing it would be illegal and would unfairly penalize refineries that are complying with biofuel requirements, according to the Bloomberg report.