This holiday season, Congress in the U.S. may be stepping into the role of the Grinch.

If lawmakers cannot come to an agreement by midnight on Saturday, the government risks a shutdown. Many Americans are worried about how this shutdown could impact their everyday lives and the festive celebrations they have planned.

A government shutdown occurs when Congress fails to authorize new funding for federal agencies. During such a shutdown, only essential services continue to operate, which include the military, public safety, law enforcement, TSA personnel, air traffic controllers, and disbursements for Social Security and Medicare.

Federal employees who are still expected to work, including millions in the military, will do so without receiving their usual paychecks. In contrast, hundreds of thousands of other federal workers would face furloughs, leading to financial strain during what is generally a joyous time of year.

Here are several ways a potential shutdown could impact Americans.

Will holiday travel be disrupted?

Air travel will still be possible during a government shutdown. TSA airport screeners and air traffic controllers from the Federal Aviation Administration are expected to report for duty. However, these workers will not receive their paychecks until a resolution is reached in Congress. During the previous shutdown that occurred over the 2018 holiday season, air traffic controllers indicated they might leave their positions, contributing to travel delays at various airports.

According to TSA administrator David Pekoske, around 59,000 of the agency’s 62,000 employees will remain on duty during a shutdown to screen travelers and maintain security at airports. However, he warned that “an extended shutdown could lead to longer wait times at airports.” The TSA anticipates screening approximately 40 million travelers this holiday season.

Additionally, passport offices in some locations may close, making it difficult for travelers needing to renew their documents or address issues prior to international trips.

Military personnel will not be paid until Congress resolves the issue

Active-duty military members stationed domestically and overseas will still be required to carry out their duties during a shutdown but will not receive their regular paychecks, as confirmed by Pentagon press secretary Maj. Gen. Pat Ryder. This also includes reservists who must fulfill their training and duty requirements.

Ryder reiterated that “the Department of Defense will continue to uphold our primary responsibility and mission to defend our nation and its citizens,” regardless of the funding stalemate.

Without a budget or continuing resolution, military personnel will miss their end-of-month pay during the holiday season. Reservists who serve after December 20 will not receive compensation for their service, nor will federal employees who are required to work during the shutdown. Historically, when Congress resolves shutdowns, they often allocate funds to retroactively pay both federal employees and military personnel.

Read more: As Shutdown Looms, $100 Billion in Disaster Relief Hangs in Balance

What will be the fate of national parks?

Most national parks are expected to close during a federal shutdown, which could disrupt vacation plans for those hoping to experience the country’s natural beauty during the holidays.

The National Park Service usually has contingency plans that involve shutting down the majority of parks and monuments. During the 35-day shutdown that began in December 2018, only a few parks, such as the National Mall in Washington, D.C., remained open, but with limited services for visitors, including fewer guides and inadequate restroom facilities. The National Park Service estimated a loss of $500 million in visitor spending during a previous 16-day shutdown in 2013.

In Utah, state officials may tap into state funds to keep national parks operational. Governor Spencer Cox criticized the ongoing congressional negotiations as “just embarrassing” and assured reporters that plans are in place to keep the five national parks in Utah open during a shutdown.

How will safety-net programs be impacted?

Programs such as the Supplemental Nutrition Assistance Program (SNAP), widely known as food stamps, and the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) will continue to provide support during a shutdown. However, federal offices managing these programs may have limited ability to assist those who need to enroll or resolve issues with their benefits. If the stalemate continues, funding for WIC and SNAP could run low.

Moreover, prolonged shutdowns could disrupt childcare programs like Head Start, which offers grants to childcare centers for families struggling to afford preschool education.

Social Security and Medicare benefits will continue without interruption. However, federal offices may experience reduced capacity to assist those wanting to enroll or address issues. Veterans Affairs benefits, including pensions and disability payments, will also continue as usual.