As Republicans on Capitol Hill struggle to pass a new federal funding deal, many federal workers are now left in limbo, waiting to see how a government shutdown would affect them with the holidays just around the corner.

Based on previous government estimates, about 3.5 million federal workers could go without paychecks this holiday season until a deal is reached – many of whom, such as airport security officers, will be required to show up for work anyway. Others could be ordered to stay home and not work.

A U.S. General Services Administration payroll plan shows some federal employees would miss their paychecks as early as Jan. 3 if a deal isn’t reached by then.

Federal contractors do not have to work and do not receive any guarantee of repayment for the duration of the shutdown.

Since fiscal year 1977, there have been 20 funding gaps lasting from just one day to 34 full days. If the government shuts down at 12:01 a.m. Saturday, it would be the 21st shutdown.

Below is a small snapshot of the impact a shutdown could have on millions of Americans across the country.

Impact on the military

About 1.3 million active military personnel would still have to work, but without pay, until a funding agreement is reached. Normally, half of the Defense Department’s 700,000 civilian workforce is expected to continue working without pay.

Generally, contractors are not required to work and lose paychecks for the duration of the shutdown.

Impact on travel

The shutdown would come at a time when many Americans are traveling for the holidays — some of the busiest travel days of the year.

According to the Transportation Security Administration, about 59,000 of the agency’s more than 62,000 employees are considered essential and would continue to work without pay in the event of a shutdown.

According to TSA, the agency expects to screen 40 million passengers over the holidays through January 2nd.

“While our staff is prepared to handle high volumes of travel and ensure safe travel, please be aware that an extended closure could result in longer wait times at airports,” TSA Administrator David Pekoske said on X.

Nearly 13,000 air traffic controllers would likely work without pay, and the hiring and training of new air traffic controllers would stop during a shutdown, according to the Department of Transportation’s latest planning document.

It’s worth noting that air traffic controllers played a role in ending the government shutdown in 2019, when several workers called in sick on the same day, paralyzing air traffic. Then-President Donald Trump announced an agreement to temporarily reopen the government on the same day.

Impact on the border

An estimated 60,971 U.S. Customs and Border Protection employees and 17,575 Immigration and Customs Enforcement employees would be required to work without pay during a shutdown, according to the Department of Homeland Security’s latest planning document.

Would the closure affect Social Security?

Because they are considered “mandatory” expenses, payments from Social Security and Medicare will continue to arrive in mailboxes, even as authorities warn that services could slow.

Could holiday mail be affected?

The US Postal Service will also not be affected because it is an independent agency and relies on its own source of revenue.

Americans could see other effects

Since the shutdown would begin on a Saturday, many Americans would not truly feel the effects of a shutdown until Monday.

The National Park Service said it “remains confident that a loss of federal funding will not occur,” but if it does, “routine visitor services will be available through Sunday.” They are still reviewing the agency’s emergency plan and working on details for individual parks.

The Smithsonian Institution, which operates 21 museums and the National Zoo in Washington, D.C., planned an announcement Friday with further guidance on the impact of a closure, a spokesman told ABC News.