Story highlights Rep. Steve Israel says the riders added to the legislation are a "poison pill"

Congress must pass a bill by Thursday at midnight to keep the government open

Dem backlash is throwing spending deal into doubt

A backlash from Democrats over add-ons to a massive government spending bill is throwing passage of the measure into doubt and once again raising concerns about a government shutdown.

The House is slated to vote on the legislation Thursday, just hours before agencies run out of money. But on the morning of the scheduled vote, Rep. Steve Israel, a member of Democratic leadership, said the riders in bill have become a "poison pill" against Democratic support that the GOP majority needs for the measure to pass.

"At this point I don't see many Democratic votes at all for a bill that is so antithetical to the middle class," Israel told CNN following a meeting with other Democratic leaders.

The $1.1 trillion spending bill authorizes funding for virtually all agencies through September, but some Democrats on Capitol Hill are vowing to oppose the legislation, arguing that the addition of some key policy changes amount to a giveaway for big special interests. Congress must pass some type of legislation by Thursday at midnight to avert a shutdown.

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The top concerns from Democrats center on a proposal to ease banking regulations in the Dodd-Frank law and a measure that would allow wealthy donors to give considerably more money to the political parties.

House Minority Leader Nancy Pelosi said the provisions were "destructive to middle class families and to the practice to our democracy" and demanded they be stripped out of the bill. Pelosi's position is critical because House Republicans need Democratic support for the measure to pass.

Though Republicans hold a significant majority in the House, Speaker John Boehner is expected to lose anywhere from 40 to 60 conservatives in his party who oppose the bill because it doesn't block the President's immigration executive action. Democrats will need to provide votes to offset those losses, setting up the sort of political brinksmanship that has become typical in Washington.

A shutdown remains unlikely because lawmakers could agree at the last minute to approve a bill that would keep the government running for a few months -- when Republicans will have full control of Congress.

House GOP aides say they are surprised Pelosi and others are lobbying for changes, since Democrats signed off on the bill before its release.

House Majority Leader Kevin McCarthy, asked by CNN if he was concerned about the bill's prospects, said no, replying with a smile, "do I look worried?"

Key Senate Democrats are also blasting the deal.

Sen. Dick Durbin of Illinois, the second ranking Democrats who is in charge of counting votes, said he didn't know if he would support the compromise or how many Democrats would. He called the Dodd-Frank provisions "awful."

"It is just an invitation for another financial disaster and the Republicans are hell-bent on getting that included," Durbin told reporters in the Capitol.

"Their appetite is whetted by the Nov. 4th election to undo Dodd-Frank. That has been one of their passions, second only to repealing the Affordable Care Act, and it means that the Wall Street interests -- the big banks, you know -- they're back on top as far as the House Republicans are concerned," he said.

Sen. Elizabeth Warren, the liberal Democrat from Massachusetts who is heavily involved in banking regulations, lashed out at the changes to the banking rules.

"The House is about to vote on a budget deal -- a deal negotiated behind closed doors that slips in a provision that would let derivatives traders on Wall Street gamble with taxpayer money and get bailed out by the government when their risky bets threaten to blow up our financial system," she said in a passionate floor speech. "These are the same banks that nearly broke the economy in 2008 and destroyed millions of jobs."

She urged Democrats to oppose the spending bill until "this risky giveaway is removed from the legislation."

On the campaign finance matter, House Speaker John Boehner said larger individual donations to the parties are needed because Congress had recently eliminated taxpayer funds for political conventions.

"The Congress is very concerned about taxpayer funding of political activities," Boehner said. "This provision was worked out in a bipartisan way to allow those who are organizing conventions the opportunity to raise the money from private sources as opposed to using taxpayer funds."

Republican aides familiar with the negotiations say that both the chairs of the Republican National Committee and Democratic National Committee supported the change on contributions limits to boost their own coffers.

But DNC Chair Debbie Wasserman Shultz told CNN it was "absolutely not" true that she knew anything about the change to campaign finance laws being added to the spending bill.

She said there was a joint effort with the RNC to appeal to the Federal Election Commission to raise the cap for donors for conventions, but she did not support putting this provision in the funding bill.

Democratic aides say it's still early to gauge how many members will vote no on Thursday, but acknowledge that the deal was brokered by Democrats and Republicans over several weeks. Democrats who negotiated the deal defended the end result, saying Republicans had pressed for six different changes to Dodd-Frank but Democrats were able to whittle it down to one. Democrats also said they successfully removed more than two dozen environmental items and a handful of gun-related policy provisions sought by Republicans.

Maryland Rep. Chris Van Hollen, a top Pelosi deputy, said he's voting no, and described the opposition as "running deep and getting deeper" as more Democrats review the details.

The number three House Democrat, South Carolina Rep. Jim Clyburn, told reporters he was undecided, but was hearing "lots of concerns" about the banking provision, and said "a lot of civil rights groups have been burning up the airwaves with problems about this."

A similar measure removing this same financial regulation was passed by the House last October, with 70 Democrats voting for it, a point McCarthy noted on Wednesday when pressed about the latest criticism from Democrats

"Do they want to shut down the government?" McCarthy said about those Democrats vowing to oppose the spending measure.

Boehner's spokesman said the controversial provisions will remain in the bill.

"If Rep. Pelosi doesn't think her negotiators did a good job, she should discuss it with them - but sour grapes doesn't mean she gets to rewrite the deal after the fact," Michael Steel said in a statement to CNN.

Still Republicans insist that there won't be a shutdown over this issue, and indicated they would consider a short-term funding bill through early next year -- when they will have full control of Congress -- if this bill fails.