A government shutdown is days away. Here’s what you need to know.

Funding for federal agencies expires on Sept. 30, and Congress is at an impasse over how to avert a government shutdown.

That means broad swaths of the federal government - from national parks to small business loans to taxpayer services - are set to go offline this week until lawmakers and President Donald Trump strike a deal on new funding.

This shutdown, if it happens, could be different from other recent shutdowns: The White House budget office has told agencies to consider broad layoffs if the government closes.

Here’s what you need to know.

What is a government shutdown?

The federal government can only spend money that is approved by Congress through spending laws called appropriations. Congress typically passes spending bills that expire at the end of the fiscal year, Sept. 30.

When that funding lapses, and there is not another appropriation to take its place, federal agencies are forbidden from spending additional money, forcing them to shut down until a new funding law is enacted.

Why is the government about to shut down?

Republicans control both chambers of Congress, but they need help from Democrats in the Senate to bypass a filibuster. House Speaker Mike Johnson (R-Louisiana) and Senate Majority Leader John Thune (R-South Dakota) have proposed a seven-week stopgap funding bill, called a continuing resolution or CR, to avert a shutdown. It would extend current funding at levels first set under President Joe Biden, adding millions for new security across the federal government to address concerns after conservative activist Charlie Kirk was killed. The House has already passed the measure; it lacks sufficient Democratic support in the Senate. Democrats want it to include provisions to extend subsidies for Affordable Care Act insurance plans that will expire at the end of the year, as well as restore some Medicaid funding cut in the GOP’s tax law this summer.

The CR is designed to give negotiators time to come to a broader agreement on year-long appropriations, but Trump’s claims of authority to intervene in the spending process scuttled those negotiations largely before they started.

Trump and White House budget director Russell Vought have asserted broad power to ignore spending laws and block money from leaving federal coffers for programs not in line with the administration’s positions, a process called impoundment. The administration also angered Democrats with its successful push to get Congress to cancel spending it had already approved for public broadcasting and foreign aid.

Democrats contend that impoundment is illegal under a post-Watergate-era law; the Constitution grants spending power exclusively to Congress.

The dispute has left lawmakers in what some feel is a no-win position. If Congress approves new appropriations, Trump could impound funds for policies he disagrees with. And without new appropriations, the government will shut down, giving the White House latitude to decide which “essential” services will remain operational even when funding has lapsed.

How long would a government shutdown last?

It’s impossible to know how long a shutdown could last. The shortest government shutdown lasted just a few hours. The longest shutdown occurred in Trump’s first term and lasted 34 days.

The early indications from lawmakers in Congress are that a shutdown this time around could go on for a while, and the logistical elements of the congressional calendar are lining up that way, too.

Democrats, cowed by criticism from their left flank about the last spending deal they cut with Trump in March, are adamant there will be no agreement unless Republicans negotiate with them on rolling back cuts to health care programs. Republicans counter that Democrats don’t have much leverage in the negotiations to begin with.

The shutdown deadline hits midweek, which is not insignificant. Congress usually tries to position deadlines on a Friday, so if funds lapse, lawmakers can hash out a deal over the weekend before federal workers head back to the office. In this case, the deadline is midnight Tuesday into Wednesday, meaning there’s no buffer built into the calendar.

How will federal agencies deal with a shutdown?

Traditionally, federal agencies prepare plans for a government shutdown and post them publicly on the Office of Management and Budget website. Those plans show which federal services would continue under a shutdown. Employees whose jobs are necessary for public safety and protecting government property continue to work - unpaid - during shutdowns, while other employees are furloughed.

But this is not shaping up to be a traditional shutdown.

OMB on Wednesday told agencies to prepare to fire employees who are not considered “essential,” a threat that would dramatically and almost immediately downsize the headcount and capabilities of the federal workforce.

The only agencies not affected, OMB said, would be those that received funding through Trump and Republicans’ One Big Beautiful Bill, the $4.1 trillion tax and immigration law that passed Congress in July. That includes the Defense Department, the Department of Homeland Security and the Federal Aviation Administration.

Federal functions that receive funding through other sources and don’t rely on annual spending laws from Congress, such as Social Security, Medicare and veterans health care, also would not be part of the layoffs.

Once a government shutdown ends, OMB said, agencies should revise their layoff plans “to retain the minimal number of employees necessary to carry out statutory functions.”

Do national parks close during a government shutdown?

National parks usually close during a government shutdown, but it’s unclear how broad that closure will be.

Visitor services - bathrooms, visitor centers, trash collections and park ranger services - will not be available. During past shutdowns, some parks themselves remained open to visitors without those services. In others, the parks closed entirely.

The National Park Service generally asks people not to visit during shutdowns because of potential safety concerns.

Will payments to Social Security recipients be affected?

Social Security benefits continue during a government shutdown. The Social Security trust fund receives revenue directly through payroll taxes, not appropriations.

Operations at the Social Security Administration, though, may be affected. The administration will furlough - or could prepare to fire - thousands of people who work on IT projects, replace Medicare cards and process account questions, like overpayments.

Does mail delivery continue during a government shutdown?

Mail delivery continues during a shutdown. The U.S. Postal Service funds its operations through the sale of postage products, mail and packages, and through a line of credit from the Treasury. It does not receive appropriated funds.