Large swaths of the U.S. federal government began closing down at midnight Monday after the House and Senate failed to find a compromise on a spending bill to fund the government.
The shutdown will idle as many as 1-million federal employees and affect everything from economic data releases to National Park admissions.
Here's a look at what will be affected:
For Canadian business leaders, the greatest concern is that border crossings may be affected, even though they fall under one of the "essential services" categories that are exempted from the shutdown.
According to contingency plans filed by the Department of Homeland Security, port-of-entry operations and border patrols are not supposed to be affected. Similarly, air traffic control services will be exempted from the shutdown, the Department of Transportation says.
But it isn't entirely clear what will happen at border crossings and ports, where any delays would have immediate impact on Canada's economy.
"I don't think they know themselves [what will happen]," said Jayson Myers, president of Canadian Manufacturers and Exporters.
Economic data and markets
Much of the publication of economic data will stop. This includes the closely watched monthly employment report and the Agriculture Department's important Oct. 11 U.S. crop report.
The U.S. Securities and Exchange commission will not be affected right away. It can continue reviewing applications for initial public offerings and monitoring markets as normal for a few weeks, a spokesman said.
Bank regulators, including the Federal Reserve and the Consumer Financial Protection Bureau, would stay open because they do not rely on Congress for funding.
National parks and museums will shut down, including iconic locations such as the Statue of Liberty and Yellowstone National Park. Guests staying in park campgrounds will be given 48 hours to make alternate arrangements and leave.
In Washington, all Smithsonian Institution locations will shut down. The Smithsonian's National Zoo said it would even turn off its website's livestreaming videos from the animals' pens – including a popular "Panda Cam" of a newborn cub.
The Centers for Disease Control's annual seasonal flu influenza program will be shuttered.
Medical research at the National Institutes of Health will stop, but staff will remain to tend to 1.3 million lab mice, 63,000 rats and 3,900 monkeys. "Many of these animals are priceless and have taken generations to breed," the U.S. Department of Health's contingency plan says.
Food and Drug safety
The FDA will be unable to support the majority of its food safety activities, including routine establishment inspections and monitoring imports, according to the U.S. Department of Health's contingency plan. It will also cease monitoring cosmetics and will be unable to monitor imports.
USDA meat inspectors stay on the job.
All military personnel would continue on normal duty status, but half of the Defense Department's 800,000 civilian employees would be placed on unpaid leave. Officials have said military personnel, who are paid twice a month, would receive their Oct. 1 paycheques but might see their Oct. 15 paycheques delayed.
Internal Revenue Service
Most of the federal tax agency's 90,000 employees are being furloughed.
Those assigned to vital national security missions, including supporting the president, and collecting data from informants or spy devices such as eavesdropping systems or satellites, will generally remain on the job.
Courts and the Justice Department
The U.S. Supreme Court would probably operate normally, but the status of federal courts will have to be assessed after about 10 business days. Criminal litigation will continue, while civil litigation is 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.
The Environmental Protection Agency is one of the hardest-hit, with less than 7 per cent of its employees exempt from furlough. The shutdown of all but emergency services would delay rule-making, potentially including finalization of renewable fuel volume requirements for 2014.
Most of the National Aeronautics and Space Administration's 18,250 personnel will be furloughed, save for about 550 people who deal with operations aboard the International Space Station and ongoing satellite missions.
The White House
The Executive Office of the President will furlough about 1,265 staff and retain 436 as excepted workers. Among the staff retained will be 15 to provide "minimum maintenance and support" for the White House. Executive agencies will be reduced to skeleton staff, including four at the Council of Economic Advisors.
The program at the heart of the standoff between politicians will still start operating. Signup for the new U.S. health exchanges under the Affordable Care Act that were due to start on Oct. 1 will proceed.
With a report from Reuters