Much of the U.S. government is closed for business for the first time in 17 years after Congress failed to agree on a temporary spending bill to keep it operating.
About 800,000 federal workers are on furlough, while other federal workers are staying on the job with no guarantee when they will be paid.
The Republican-led House of Representatives approved three spending bills that would delay enactment of the Obama administration's new health insurance plan, and the Democratic-controlled Senate rejected the bills because they were linked to so-called "Obamacare." The Senate rejected a House request for negotiations early Tuesday.
The shutdown will not affect the schedule of Voice of America broadcasts, but will close national parks, traffic safety agencies, and lay off most Defense Department civilian employees. But the U.S. military will remain on duty, and ongoing military operations like those in Afghanistan will continue.
Homeland Security agents and border security offices will remain open, as well as other law enforcement agencies. Enrollment for "Obamacare" also began as scheduled Tuesday.
Experts say a shutdown of more than two weeks is likely to slow the U.S. economy through reduced tourism cash flow and furloughed federal workers curtailing their personal spending.
Democrats say the new health care law gives low-income families and people without health insurance the chance to buy a low-cost, federally-subsidized policy to prevent financial ruin in case of serious illness.
Republicans say the program is confusing and not ready. They also say the law hurts the economy by imposing more taxes and by forcing small businesses to provide coverage for their employees.