WASHINGTON -- Tax credits for clean energy sources won’t hitch a ride on legislation reauthorizing the Federal Aviation Administration in the Senate, and Democrats say conservative mega-donors Charles and David Koch are to blame.

Legislators agreed to an extension of tax credits for geothermal, small wind, fuel cells, and combined heat and power in the large omnibus spending deal passed last year, but the provisions were left out due to a "drafting error." The understanding between both parties was that the credits would need to be included in another must-pass bill in the new year. The aviation bill provided an opening to settle the score, but on Tuesday, party leaders said negotiations to include the tax credits crumbled.

Talking to reporters, Senate Minority Leader Harry Reid (D-Nev.) pointed to his face, and said, “Would you please mark, I’m trying to smile; this is so ridiculous.”

Asked if Democrats were pushing to include too much in the FAA bill, Reid said they weren’t trying to add “all that garbage” that Republicans were bringing to the table, including tax provisions on beer.

“All we did as far as our part of the bill went, we did what [Senate Majority Leader Mitch] McConnell made a mistake in,” Reid said of the initial omission in the omnibus. “No one is saying he cheated, or did it willfully.”

After party lunches on Tuesday, McConnell (R-Ky.) said the underlying legislation was on a clear path, but that leaders “made a decision to skinny down in effect the tax part.”

Democrats pointed to a letter sent to the Finance Committee by 30 conservative organizations, including Koch-affiliated groups Americans for Prosperity and Heritage Action. In it, the groups voiced opposition to including an extension of the renewable tax credits in the FAA bill.

“The reason it went down, the reason it went down is the Koch brothers pay for 34 different groups that look like their environmental groups -- of course they’re not -- they’re the ones that killed this bill, they’re the ones that killed the bill,” Reid said.

Cutting Reid off, Sen. Chuck Schumer (D-N.Y.) tried to further hammer the point home, saying that if the tax provisions had been attached to the bill, there wouldn't have been enough support for the legislation on the Republican side.

“They were short for votes desperately, particularly after the Koch brothers made it clear they’re against any modifications in terms of clean energy no matter what is added to the bill,” Schumer said.

“Can you imagine the Koch brothers, the power they have over what’s going on in this world of ours?” Reid continued. “The tax provision ... that has thousands of jobs that will be eliminated because of the Koch brothers.”

Reid said he will still vote to move the FAA bill forward, and wait and see if McConnell adds the clean energy tax credits to different legislation later.

Freedom Partners, one of the conservative groups to urge the Senate to keep the tax credits out of the FAA bill, praised the upper chamber for dropping negotiations.

“Americans oppose corporate welfare and they’re tired of lawmakers handing out special benefits to the well-connected," said Andy Koenig, of Freedom Partners. "Congress is right to reject this backroom deal and move ahead with a clean FAA extension.”

Sen. Ron Wyden (D-Ore.) a lead negotiator on the FAA bill, expressed concern a few days ago over the hit the industry would take if the credits aren't extended.

“Some of my colleagues have told me that plants are going to close if this doesn’t get worked out quickly,” Wyden said.