Much of the U.S. government has been shut down for the first time in 17 years, after the two branches of Congress failed by the October 1st deadline to agree on a single spending bill to keep the government operating.
Thousands of federal workers are arriving at their jobs and being told they are on furlough and being sent home.
Other federal workers, considered essential, are being told to stay on the job but there is no guarantee when they will be paid.
The shutdown comes on the first day of open enrollment for health care plans according to the Affordable Care Act, the controversial U.S. health care reform nicknamed "Obamacare."
Three times on Monday, the Republican-led House of Representatives approved a spending bill that would delay enactment of the new health plan, and in all three cases, the Democratic-controlled Senate rejected it minutes later.
Shortly before midnight, White House Budget Director Sylvia Burwell issued a directive to federal agencies to "execute plans for an orderly shutdown."
While the shutdown will not affect the schedule of Voice of America broadcasts, it does mandate the furlough of an estimated 800,000 U.S. federal workers. Agencies affected will include national parks, traffic safety agencies, and the Defense Department -- mainly the furlough of its civilian employees. Homeland Security agents and border security offices will remain open, as well as other law enforcement agencies. Enrollment for "Obamacare" will also begin as scheduled.
In a video statement early Tuesday, U.S. President Barack Obama said members of the U.S. military will remain on duty and ongoing military operations like those in Afghanistan will continue. He said he plans to sign into law a bill that will ensure members of the military are paid on time. Mr. Obama also pledged to work to get Congress to reopen the government.
Experts say a shutdown of more than two weeks is likely to slow down an already sluggish economy, through reduced tourism cash flow and furloughed federal workers curtailing their personal spending.
Later Tuesday, President Obama will speak about provisions of the health care program that are being activated despite the shutdown. Many Americans who lack healthcare insurance will be able to sign up for subsidized policies on newly created insurance exchanges.
Earlier, the president said shutting down the government is the height of irresponsibility and throws a wrench into the gears of a recovering economy.
He accused House Republicans who want to defund his health care program of appealing to the right-wing Tea Party faction and re-fighting the 2012 presidential election.
The president said the entire country would feel the effects of a government shutdown -- not just federal employees who would not get paid, but citizens who rely on sometimes life-saving government services.
Mr. Obama stressed that his health care program is the law of the land -- passed by Congress, approved by voters, and upheld by the Supreme Court. He said the law will be implemented Tuesday no matter what Congress does.
He rejected proposals to postpone Obamacare, saying it would lead to another fight just a few months from now.
Democrats say the 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.