The White House and U.S. Congress have until Friday to agree to a federal spending-cut bill or face a partial shutdown of the U.S. government the next day.
Republicans and Democrats say they want to avoid a shutdown, which could idle hundreds of thousands of federal workers, close national parks and Washington's Smithsonian Institute museum complex and force the cancellation of the U.S. capital's cherished annual cherry blossom parade this weekend.
The federal work force numbers around 4.4 million, including members of the U.S. military. It has been 15 years since the last government shutdown over spending disagreements.
Here are some facts about what could happen:
* Based on the last shutdown, from December 16, 1995 until January 6, 1996, around 800,000 federal workers would be furloughed, including a "significant number" of civilian contractors working for the Defense Department, senior Obama administration officials say.
* Vital U.S. services such as national defense, law enforcement, emergency medical care and air traffic control would continue.
* The military continues to work and earn. But paychecks would be delayed after April 8 for the duration of the shutdown because the government would not have funds to make payroll.
* Unlike the last two shutdowns, both of which occurred in the 1990s, this one would take place during tax preparation and filing season. This would delay tax refunds to 30 percent of Americans who filed a paper - rather than electronic - tax return. Electronic tax collection and refunds would continue. IRS tax audits would be suspended.
* National parks and museums would close.
* Social Security and Medicare benefits would continue to be paid.
* Federal activities with separate sources of money like user fees, or funds authorized on a multiyear or permanent basis, would escape a shutdown.
* During the last shutdown, an estimated 200,000 applications for U.S. passports went unprocessed and work on more than 3,500 bankruptcy cases was suspended.
* New patients would not be accepted into clinical research at the National Institutes of Health, although clinical trials that are already in progress would continue.
* The Small Business Administration's approval of applications of business loan guarantees and direct loans to small businesses would stop.
* The Federal Housing Administration would not be able to guarantee loans, potentially hurting the housing market.
* Polls show the public would hold Democrats and Republicans equally to blame for any shutdown. Both parties insist that they want to keep the government open.
(Sources: White House Office of Management and Budget, the Congressional Research Service, congressional aides, senior Obama administration officials)
(Reporting by Alister Bull and Thomas Ferraro; Editing by Paul Simao and Vicki Allen)