The ethanol industry's top proponent in the Senate will not attend a key meeting at the White House Thursday among President Trump, members of his Cabinet, Sen. Ted Cruz, and other oil state lawmakers to discuss the future of the biofuel mandate.

"Sen. [Chuck] Grassley wasn’t invited, so he’s not going to any meeting at the White House tomorrow regarding the [Renewable Fuel Standard]," said Grassley spokesman Michael Zona in an email to the Washington Examiner.

Some refiners say leaving the Iowa Republican out of the meeting limits what can be achieved at the gathering. The meeting comes after the Trump administration last week enacted new renewable fuel targets for 2018 at higher levels than oil refiners had wanted while formally rejecting a scheme to cut refiners out of the RFS altogether.

The meeting would have "more juice" if Grassley were there, said Stephen Brown, vice president of federal affairs for the large refiner Andeavor, formerly Tesoro.

Brown, who has been in talks with White House officials in recent days ahead of the meeting, said the administration needs a deal that ends the "hostage taking" over Trump nominations. Grassley and other members of the Senate had blocked several of Trumps energy and environment nominations because of the administration's earlier proposal to curtail the RFS blending requirements.

The president and Environmental Protection Agency chief Scott Pruitt responded to nomination holdups with guarantees to Grassley and Sen. Joni Ernst, R-Iowa, that he would not cut the standards, which resulted in the release of the nominations.

But Cruz, a Texas Republican, and others looking for RFS relief for refiners in their states continue to hold up Iowa Agriculture Secretary Bill Northey's appointment to serve in a top position at the Department of Agriculture. Cruz had hoped the hold would bring the Iowa delegation to the table, according to a recent letter he sent to the Iowa governor.

“We are interested in having a constructive conversation for sure” that ends “the trench warfare,” Brown said. The industry will not attend the meeting, just lawmakers, Trump and members of his Cabinet with their top advisers.

Brown said the White House is looking to float a new plan that looks to resolve refiners' issues with buying expensive Renewable Identification Number credits, which some in the refining industry have said will force them to shed jobs if a solution isn't created. Andeavor is not in that camp.

Brown had led the pushback against a plan by former Trump adviser Carl Icahn to free independent refiners from having to buy the credits to meet the standard.

He said the White House is not planning to resurrect the Icahn proposal, nor is it resurrecting an idea suggested by the EPA to reduce the RFS blending requirements beginning in 2019. But that's the only thing that is clear about the new RIN proposal, Brown said.

The White House said it would not comment on the meeting or give any details until Thursday.

Reuters reported that the meeting could set the stage for negotiating legislation that looks to reform the renewable fuel program. Sen. John Cornyn, R-Texas, is looking at drafting legislation on the RFS, according to an industry source. Cornyn had joined Cruz in a letter that senators sent to Trump in October asking for a White House meeting between the refiners and the ethanol industry.

Cornyn is said to be looking to release a draft bill next year, the source said. But details are being kept close to the vest. Cornyn's office could not be reached for comment.

No ethanol groups are attending the meeting, according to the White House.