Obama, meanwhile, has not yet signaled whether he would sign the measure. At the White House on Wednesday, press secretary Josh Earnest acknowledged that "this is a compromise proposal. Democrats and Republicans have signed onto it. And ... I'm confident that there are going to be some things in here that we're not going to like. And so we'll have to sort of consider, you know, the whole package before we make a decision about whether or not to sign it. So we'll keep you posted on that."
Warren and Rep. Maxine Waters of California held a joint press conference on Wednesday, urging House Democrats to vote against the omnibus as long as it includes the Dodd-Frank provision. Waters, who called the move "unconscionable," noted that if House Republicans need Democrats to join them in passing the omnibus, she and her colleagues would have significant "leverage" to remove the provision from the underlying bill.
Both Democrats expressed shock that the measure had made it through the Appropriations Committee process. "I want to find out from, I'm sorry, Ms. Mikulski on Appropriations—why did this get in?" Waters said in a reference to the Senate panel's chairwoman, Barbara Mikulski.
Waters and Pelosi both urged their fellow California Democrats to oppose the bill at a delegation meeting Wednesday.
Democratic appropriators have argued that Republicans floated many worse provisions affecting Dodd-Frank and other Democratic programs, the majority of which they were able to keep out of the omnibus. The final omnibus may not be perfect, they argue, but it's better than it could have been.
Warren said she understood the nature of compromise, but she argued that the swaps provision was too much to swallow. "They've gone too far. This is just one step too far. And we can't pass an omnibus with this provision in it," she said.
Ultimately, though, Warren stopped short of saying she would hold up the bill in the Senate if the omnibus makes it through the House as is. "I am opposed to this, I've already been to the Senate floor [to speak] on this, I will be back on the Senate floor about this," Warren said. "The House has the opportunity here to say no."
House Budget Committee ranking member Chris Van Hollen said Wednesday he will also vote against the bill, partly because of the campaign finance provision, which would allow big donors to make maximum donations to several different accounts established by the same party committee and thus significantly raise the overall ceiling for what an individual donor can give.
Meanwhile, Rep. David Price, ranking member of the Homeland Security Appropriations Subcommittee, said he is inclined to vote against the bill as well, mostly because it extends funding for DHS only into February, but also because of the two riders.
"I think it's very damaging. I think it's a poor way for us to do business as appropriators," he said. "The substance is bad, and the process is worse. That's enough to tip my vote."
Party liberals are also concerned. "If the language of this bill does not change, the Congressional Progressive Caucus will oppose it," said a source within the group.
Rachel Roubein and George E. Condon Jr. contributed to this article