A U.S. government shutdown is possible on Tuesday, the first day of fiscal 2014, because Congress has so far failed to find a way to pay for it.
A closure would have far-reaching consequences at federal agencies dealing with everything from sending out Social Security checks to collecting admission fees at national parks.
Here is a roundup of how the impact would be felt:
Federal workers: As many as 1 million U.S. federal employees could face unpaid furloughs or payless paydays, according to the president of the American Federation of Government Employees, which represents 670,000 union members.
National parks: National parks would close, meaning a loss of 750,000 daily visitors and an economic loss to gateway communities of as much as $30 million for each day parks are shut, according to the non-profit National Parks Conservation Association.
(Read more: Last shutdown is a lesson lost on Capital Hill)
Defense Department: All military personnel would continue on normal duty status, but many civilian employees would be temporarily furloughed, Deputy Defense Secretary Ashton Carter said in a memo. He said furlough notices would be issued on Tuesday, Oct. 1, if no agreement to fund the government is reached.
The ratings agency Standard & Poor's said a shutdown of less than two weeks would not materially affect the credit of big defense contractors, though a longer shutdown could weaken smaller defense contractors. Most defense contractors would not be paid, new contracts would not start and orders would be delayed, with service contracts hardest hit, S&P said.
Internal Revenue Service: Most of the federal tax agency's 90,000 employees would be furloughed. Taxpayers who requested an extension beyond the April 15 deadline to file their 2012 taxes must do so by Oct. 15, and they will still be able to file these returns even if the IRS is still shut down then.
Federal Reserve and other financial agencies: The Fed would stay open, since it does not depend on congressional appropriations to operate; so would the Consumer Financial Protection Bureau, which the Fed funds. The Federal Deposit Insurance Corp and the Office of the Comptroller of the Currency pay for themselves and would remain open. The Commodity Futures Trading Commission has been rushing through approvals for a new, untested type of trading platform ahead of a possible shutdown, its top regulator said.
Justice Department: Fewer than 18,000 of the department's 114,486 employees would be furloughed, and if the furlough is prolonged, some of those could be brought back to work. Criminal litigation would continue under a government shutdown, while civil litigation would be curtailed or postponed as much as possible "without compromising to a significant degree the safety of human life or the protection of property," the department said in its contingency plan.
(Read more: Wall Street: What's the worst that could happen)
Courts: The U.S. Supreme Court would probably operate normally, as it has during previous shutdowns, but a spokesman declined to share the high court's plans.
Federal courts would remain open for approximately 10 business days if the government closes on Oct. 1, and would reassess on or about Oct. 15.
National Institutes of Health: The agency's research hospital in Bethesda, Maryland, would take no new patients.
U.S. Trade Representatives office: Already squeezed by automatic spending cuts imposed by so-called sequester, the USTR office has cut back on travel to the 41 countries where there are concerns about intellectual property, Trade Representative Michael Froman said.
(Read more: On the brink: Senate to meet as shutdown looms)
Environmental Protection Agency: EPA Administrator Gina McCarthy said this week that the agency would effectively shut down with only a core group of individuals available in case of a "significant emergency."
Agriculture Department: USDA meat inspectors would stay on the job, industry experts said. Statistical reports would be delayed. An Oct. 1 shutdown would come as the agency is surveying farmers and checking fields for yields and acreage in advance of the Oct. 11 crop report. A government closure of more than a few days could delay the report, relied upon by traders and food manufacturers as the best estimate available of the U.S. food supply.
Washington, D.C, sights: Some popular tourist spots in the nation's capital would probably close, including the FDR Memorial, the Kennedy Center for the Performing Arts, the Library of Congress, the Lincoln Memorial, the National Archives, the National Zoo and all Smithsonian Museums.