The US government is hours away from a partial shutdown, its first in nearly two decades, with Republican and Democratic lawmakers trading blame over who is responsible.
Congress was closed on Sunday after an early-morning vote in the Republican-run House of Representatives to delay key parts of President Barack Obama's healthcare law.
They will be deliberately bringing the nation to the brink of a government shutdown.
Republicans have refused to pass a budget unless Democrats agree to the concessions.
The Senate is scheduled to convene on Monday afternoon, just hours before the shutdown deadline at midnight, and majority leader Harry Reid has already promised that Democrats will kill the House's latest proposal.
Barring any last-minute action, about 800,000 federal workers would be forced off the job without pay. Some critical services such as patrolling the borders, inspecting meat and controlling air traffic would continue.
Social Security, the American pension scheme, will continue to pay out benefits, and the Medicare and Medicaid healthcare programmes will continue to function as well.
The latest fiscal fight underscored the deep divide between the Republicans and the Obama administration and its Democratic allies.
Republicans insisted that the healthcare law was costing jobs and driving up healthcare costs.
Obama has said he will not let the law, his chief domestic achievement, be gutted; Democrats say Republicans are obsessed with attacking the overhaul, which is aimed at providing health coverage for millions of uninsured Americans.
Since the last government shutdown 17 years ago, temporary funding bills known as continuing resolutions have been uncontroversial.
But with exchanges set to open on Tuesday where people could shop for healthcare coverage from private insurers, lawmakers from the Republicans' ultraconservative tea-party wing are willing to take the risk in their drive to kill the healthcare law.
The action in Washington on Sunday was limited mainly to TV talk shows and barrages of press releases, as Democrats and Republicans rehearsed arguments for blaming each other if the government in fact closes its doors at midnight on Monday.
"You're going to shut down the government if you can't prevent millions of Americans from getting affordable care,'' said Democratic Representative Chris Van Hollen of Maryland.
"If the Senate stalls until Monday afternoon instead of working today, it would be an act of breathtaking arrogance by the Senate Democratic leadership," said House Speaker John Boehner. "They will be deliberately bringing the nation to the brink of a government shutdown."