The U.S. Capitol during a cloudy night, on Capitol Hill in Washington, D.C., U.S., September 17, 2025. REUTERS/Daniel Becerril

By Courtney Rozen and Andy Sullivan

WASHINGTON (Reuters) -U.S. government services would be disrupted if President Donald Trump and Congress do not agree on a spending bill by midnight on Tuesday.

Hundreds of thousands of federal employees deemed to be not essential to protecting people and property would be sent home.

The impending shutdown would differ from past government closures because Trump has threatened to lay off more federal workers if lawmakers do not pass legislation to avert the closures. His administration has not outlined what cuts to expect.

"We will be looking for opportunities" to reduce the size of the federal government, said White House budget director Russ Vought in a television interview.

As of Tuesday afternoon, at least 21 of the 23 largest federal agencies posted details about which employees they would furlough. Here is a guide to what would stay open and what would close in a government shutdown, according to plans released so far:

WHEN AND WHY WOULD THE GOVERNMENT SHUT DOWN?

Congress writes detailed spending legislation for most U.S. government agencies each year, but rarely finishes before the fiscal year starts on October 1. Lawmakers typically pass stopgap spending bills to avoid disruption for several weeks or months while they finish their work.

The current stopgap bill is due to expire on September 30. Republicans and Democrats appeared unlikely to reach an agreement on some sort of extension that Trump would sign into law before midnight on Tuesday. This would mean wide swaths of the government would lack funds to continue their operations.

WHAT HAPPENS TO SOCIAL SECURITY, MEDICARE AND MEDICAID?

The Social Security Administration would keep issuing retirement and disability benefits, but would furlough 12% of its staff and pause marketing campaigns, according to the agency’s shutdown plan.

Payments would likewise continue under the Medicare and Medicaid healthcare programs.

WILL FOOD AID BE CONTINUED UNDER SNAP AND WIC?

The Supplemental Nutrition Assistance Program, the nation's largest food aid program, and the Special Supplemental Nutrition Program for Women, Infants and Children, known as WIC, would continue operations during a shutdown as funds allow, according to a shutdown planning document published by the U.S. Department of Agriculture.

DOES THE MAIL GET DELIVERED IF THE GOVERNMENT CLOSES?

The U.S. Postal Service would be unaffected because it does not depend on Congress for funding, USPS said in a statement. Post offices will be open.

WHAT DOES A SHUTDOWN MEAN FOR THE INTERNAL REVENUE SERVICE?

The IRS will be fully staffed for five days, according to agency shutdown plans published Monday.

The strategy does not say what the IRS, which lost about a quarter of its staff this year and now employs about 75,000 people, would do if the shutdown lasts longer than five business days. An agency spokesperson declined to comment.

WHAT ABOUT THE AIRPORTS?

More than 13,000 air traffic controllers would continue working, but without pay until the shutdown ends, according to the Federal Aviation Administration.

Most TSA employees would continue working, according to an agency statement.

WILL FEDERAL COURTS BE FULLY OPERATIONAL?

Last week, the federal judiciary warned that the courts could run out of money to fully sustain operations as soon as Friday if Congress fails to pass a spending bill.

That is a shift. The courts sustained operations for five weeks when the government shut down during Trump's first term.

WHAT DOES A SHUTDOWN MEAN FOR THE MILITARY?

The 2 million U.S. military personnel would remain at their posts without pay until the shutdown ends, according to a Department of Defense statement.

National Guard forces Trump has deployed to U.S. cities must also continue to work.

Contracts awarded before the shutdown would continue, and the department could place new orders for supplies or services needed to protect national security.

Trump has ordered the department to rename itself the Department of War, a change that will require action by Congress.

HOW DOES A GOVERNMENT SHUTDOWN AFFECT LAW ENFORCEMENT?

Agents at the FBI, the Drug Enforcement Administration, Coast Guard and other federal law enforcement agencies would remain on the job.

WHAT HAPPENS TO BORDERS AND HOMELAND SECURITY?

Justice Department staff that administer the immigration court system will largely stay on the job because Trump declared illegal immigration a national emergency, according to a department statement.

Employees that communicate with state and local officials about immigrant arrests would also keep working, according to the statement. Border patrol and immigration enforcement agents would stay at their posts, as would most customs officers, according to the Department of Homeland Security’s shutdown strategy.

Tariff collections would continue, according to the strategy.

DOES A SHUTDOWN DELAY KEY ECONOMIC DATA?

Publication of major U.S. economic data, including employment and GDP reports of critical importance to policymakers and investors, would be suspended.

DOES A GOVERNMENT SHUTDOWN AFFECT SMALL BUSINESSES?

The Small Business Administration would furlough 24% of its staff, according to a statement. It would not approve new loans for small businesses to buy equipment and upgrade buildings. Lending to help businesses recover from natural disasters would continue.

WHAT HAPPENS IF THERE IS A NATURAL DISASTER?

The Federal Emergency Management Agency has about $2.3 billion available in its Disaster Relief Fund, according to a September 15 report, meaning the agency should function if a hurricane or other natural disaster strikes. About 4,000 FEMA employees would be furloughed, according to an agency statement.

(Reporting by Courtney Rozen, Leah Douglas, Patricia Zengerle and Andy Sullivan in Washington; Additional reporting by Nathan Layne in New York and Nate Raymond in Boston; Editing by David Gregorio)