A last-ditch revolt against Wall Street efforts to overturn key banking reforms is threatening to derail passage of the $1.1 trillion US budget through Congress on Thursday just hours before funding for the federal government is due to expire.

Democrats in the House of Representatives have rallied around Senator Elizabeth Warren to oppose the plan, hatched with support from corporate lobbyists, which buries the clause deep in the 1,600-page omnibus spending bill and could extend future public bailouts to riskier trading activities.

Because the budget bill is also opposed by some on the right of the Republican party for delaying a fight with the Obama administration over immigration reform, the House speaker, John Boehner, may need some Democratic votes to secure passage of the omnibus bill before government funding authorisation expires at midnight on Thursday.

But the minority leader, Nancy Pelosi, has yet to say whether she will lend her support amid mounting disquiet on the left of the Democratic caucus over the Wall Street clause and other so-called “riders”, including further relaxation of campaign finance limits.

In a fast-moving effort to shore up the fragile budget agreement on Thursday morning, Republicans were hopeful they might not need more than a handful of Democratic votes if they can limit the size of their own rebellion.

The fight is likely to come to a head on Thursday afternoon with a procedural vote needed before the main budget bill, which also needs to pass the Senate, can proceed.

The risk of a repeat of last year’s government shutdown is limited due to the fall-back ability of House leaders to pass a short-term continuing resolution that would fund the government until Congress returns with a larger Republican majority in the new year.

Yet this also carries risks for Democrats and the White House, which fears it would embolden Republicans to use the budget process to attack new policy targets such as environmental and social programmes.

Nevertheless the Wall Street clause, which would overturn elements of the Dodd-Frank banking reform and grant government insurance to parts of the derivatives market, is sufficient provocation for many on the left of the party to draw a line at the current compromise.

“The House of Representatives is about to show us the worst of government for the rich and powerful,” said Senator Warren in a speech on Wednesday that served to rally opposition.

“The House is about to vote on a budget deal, negotiated behind closed doors, that slips in a deal that would let derivative traders working 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.”

Warren claims the clause was written by lobbyists for Citigroup and epitomises what is wrong with Washington’s legislative process.

“Who does Congress work for?” she added. “Does it work for the billionaires and the giant companies with their armies of lobbyists and lawyers or does it work for the ordinary people?”