Key Republicans from midwest states are threatening to hold up President Trump's EPA nominations over the administration's proposal to reduce the amount of biofuels that gets mixed into gasoline and diesel.

Sen. Chuck Grassley, R-Iowa, said Tuesday that "plenty of senators" would considering voting against the Trump administration's EPA nominees unless the agency backs off this plan.

According to the Associated Press, Grassley, in a phone call with local reporters Tuesday, was asked what leverage he had to get EPA Administrator Scott Pruitt to maintain the renewable fuel standard, or RFS, as it is.

Grassley replied: "Hold up EPA nominees. I think there's plenty of senators would do that."

The Iowa senator met with Pruitt on Tuesday to discuss his objection to the EPA's proposal to reduce targets for biofuels in 2017 and 2018 below current levels.

After the meeting, Grassley released a more subdued statement, but still threatened to "hold the administration accountable" if he doesn't get his way.

"I'll oppose any effort to reduce blending levels or undermine the integrity of the RFS," Grassley said in a statement late Tuesday. "I'm watching this issue closely and plan to hold the administration accountable."

Grassley and other lawmakers from Midwestern states who met with Pruitt, including Iowa's other Republican senator, Sen. Joni Ernst, say the proposal would result in job losses for local farmers and manufacturers.

President Trump promised in the campaign to keep things as they are, but the biofuel industry, and lawmakers who support it, say they now feel betrayed.

The Senate Environment and Public Works Committee on Wednesday was scheduled to consider the nominations of key EPA officials, but it postponed its planned hearing Tuesday night. It's unclear if the postponement had to do with the Republican threats to vote against EPA nominees because of the administration's biofuel proposal.

The nominees scheduled for consideration include Michael Dourson, nominated to run the EPA's Office of Chemical Safety and Pollution Prevention, and Bill Wehrum tabbed to run the agency's air office.

Grassley does not serve on the Environment and Public Works Committee, but some of his Republican counterparts who do suggest Tuesday they could vote against Wehrum's nomination to run EPA's air office, citing concerns about his support for Pruitt's proposed biofuels policy.

"I'm not comfortable with him right now," Ernst, R-Iowa, who belongs to Environment and Public Works Committee, said earlier Tuesday of Wehrum.

Ernst released a noncommittal statement after meeting with Pruitt.

"Our meeting today was another clear demonstration that biofuel-producing states will never stop fighting to protect the RFS," she said. "Administrator Pruitt again claimed today that he will not do anything to undermine the program. However, we have heard this before. We now need to see it. I will continue to work with the EPA, but they must prove to the agricultural community who put their faith in this administration that they will fulfill their promise to maintain the letter and the spirit of the RFS. We will not accept anything less."

Republicans hold an 11-10 majority over Democrats on the Environment and Public Works Committee, so just one GOP defection would defeat the nominations of Wehrum and Dourson. Democrats are uniformly opposed to both nominations, citing their close ties to private industry.