(MotherJones) - Here's a quick guide to who and what will be most affected:

Anyone who might get sick: The Centers for Disease Control and Prevention (CDC) would lack funding to support its annual flu vaccination program.

Military personnel: Barring last-minute congressional action, members of the armed forces would have their paychecks put on hold while they continue to work.

People who use boats: The Coast Guard will cut back on routine patrols and navigation assistance.

Civilian defense employees: 400,000 Department of Defense employees will be given unpaid vacations.

Family members of fallen soldiers: Death benefits for military families will be delayed.

Gun owners: During the 1990s shutdown, applications for gun permits were delayed due to furloughs at the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Trees: Hundreds of US Forest Service workers face furloughs in California during peak forest fire season.

Visa applicants: Furloughs at the State Department's Bureau of Consular Affairs mean tens of thousands of visa applications are put on hold.

People traveling abroad: A shutdown would cause delays in the processing of passport applications.

Sick people: The National Institutes of Health will not admit new patients unless ordered by the director.

Factory workers: The Occupational Safety and Health Administration will halt regular inspections.

Hikers: All 401 National Park Service sites will be closed.

People who make money off tourists: Shuttered national parks are bad news for the hotels, restaurants, and other attractions that feed off them.

Small business loan applicants: The Small Business Administration will furlough 62 percent of its workforce.