A sign marks a closed corridor at the Rotunda of the U.S. Capitol.

Administration officials now live in fear of a 19th-century law that could get them fired, penalized or even imprisoned if they make the wrong choices while the government is shut down.

The law is the Antideficiency Act, passed by Congress in 1870 (and amended several times), which prohibits the government from incurring any monetary obligation for which the Congress has not appropriated funds.