The U.S. federal government is heading toward a shutdown that will disrupt many services, squeeze workers and roil politics as Republicans in the House, fueled by demands for deep cuts, force a confrontation over federal spending.

While some government entities will be exempt – social security checks, for example, will still go out – other functions will be severely curtailed. Federal agencies will stop all actions deemed nonessential, and millions of federal employees, including members of the military, won't receive paychecks.

Here is a look at what's ahead if the U.S. government shuts down on October 1.

What is a government shutdown?

A shutdown happens when Congress fails to pass funding legislation that is signed into law by the president. Lawmakers are supposed to pass 12 different spending bills to fund agencies across the government, but the process is time-consuming. They often resort to passing a temporary extension, called a continuing resolution or CR, to allow the government to keep operating.

When no funding legislation is enacted, federal agencies stop all nonessential work and will not send paychecks as long as the shutdown lasts.

Although employees deemed essential, such as air traffic controllers and law enforcement officers, still have to report to work. Other federal employees are furloughed. Under a 2019 law, those workers should receive back pay after the funding impasse is resolved.

When would a shutdown begin, and how long will it last?

Government funding expires October 1, the start of the federal budget year. A shutdown will begin at 12:01 a.m. if Congress fails to pass a funding plan that the president signs into law.

It is impossible to predict how long a shutdown would last. With Congress divided between a Democratic-controlled Senate and Republican-led House, and U.S. House Speaker Kevin McCarthy's conservatives looking to use the shutdown as leverage for spending cuts, many are bracing for a stoppage that could last weeks.

Who does a  shutdown affect?

Millions of federal workers face delayed paychecks when the government shuts down, including many of the roughly 2 million military personnel and more than 2 million civilian workers across the nation.

Nearly 60 percent of federal workers are stationed in the Department of Defense, Veterans Affairs and Homeland Security.

Federal workers are stationed in all 50 states and directly interact with taxpayers, from Transportation Security Administration agents who operate security at airports to Postal Service workers who deliver mail.

Some federal offices will also have to close or face shortened hours during a shutdown.

Beyond federal workers, a shutdown could have far-reaching effects on government services. People applying for government services like clinical trials, firearm permits and passports could see delays.

Businesses closely connected to the federal government, such as federal contractors or tourist services around national parks, could see disruptions and downturns. The travel sector could lose $140 million daily in a shutdown, according to the U.S. Travel Industry Association.

Lawmakers also warn that a shutdown could rattle financial markets. Goldman Sachs has estimated that a shutdown would reduce economic growth by 0.2 percent every week it lasted, but growth would then bounce back after the government reopens.

Others say the disruption in government services has a far-reaching impact because it shakes confidence in the government to fulfill its basic duties. The U.S. Chamber of Commerce has warned that "a well-functioning economy requires a functioning government."

What about court cases, Congress' operations and presidential pay?

The president and members of Congress will continue to work and get paid. However, any staff deemed nonessential will be furloughed.

The judiciary will be able to continue to operate for a limited time using funds derived from court filings and other fees, as well as other approved funding.

Notably, funding for the three special counsels appointed by Attorney General Merrick Garland would not be affected by a government shutdown because they are paid for through a permanent, indefinite appropriation, an area that's been exempted from shutdowns in the past.

That means the two federal cases against Donald Trump, the former U.S. president, and the case against Hunter Biden, the son of the current U.S. President Joe Biden, would not be interrupted. Trump has demanded that Republicans defund the prosecutions against him as a condition of funding the government, declaring it their "last chance" to act.

Has this happened before?

Prior to the 1980s, lapses in government funding did not result in government operations significantly shuttering. But then-U.S. Attorney General Benjamin Civiletti, in a series of legal opinions in 1980 and 1981, argued that government agencies cannot legally operate during a funding gap.

Federal officials have since operated under the understanding that they can make exemptions for functions that are "essential" for public safety and constitutional duties.

Since 1976, there have been 22 funding gaps, with 10 of them leading to workers being furloughed. But most of the significant shutdowns occurred after Bill Clinton's presidency, one being when then-Speaker Newt Gingrich and his conservative House majority demanded budget cuts.

The longest government shutdown happened between 2018 and 2019 when then-President Trump and congressional Democrats entered a standoff over his demand for funding for a border wall. The disruption lasted 35 days through the holiday season. It was also only a partial government shutdown because Congress had passed some appropriations bills to fund parts of the government.

What does it take to end a shutdown?

It's Congress' responsibility to fund the U.S. government. The House and Senate have to agree to fund the government, and the president has to sign the legislation into law.

Congress often relies on a CR to provide stopgap money to open government offices at current levels as budget talks are underway. Money for pressing national priorities, such as emergency assistance for victims of natural disasters, is often attached to a short-term bill.

But hardline Republicans say any temporary bill is a non-starter for them. They are pushing to keep the government shut down until Congress negotiates all 12 bills that fund the government, which is historically a laborious undertaking that isn't resolved until December, at the earliest.

Trump, who is Biden's top rival heading into the 2024 election, is egging on the Republican hardliners.

If they are successful, the shutdown could last weeks, perhaps even longer.

(With input from AP)