Airports: Air travel continued without interruption Tuesday as more than 14,000 air traffic controllers were ordered to remain on the job without pay.

Mail: Mail will continue to be delivered, as the U.S. Postal Service is an independent agency.

National Parks: All national parks are closed

Social Security, Medicare, Medicaid, and Unemployment Insurance: All are considered mandatory spending and will be paid. But new applicants might not have their applications processed until the government reopens.

IRS: Tax filers facing an Oct. 15 deadline will find the phone lines at the Internal Revenue Service dead.

Military: President Obama signed a bill that ensures that certain members of the U.S. military and U.S. Coast Guard will be paid during a government shutdown late Monday.