Here, I found it.

(a) Whoever, by any fraud or false pretense, enters or attempts to enter--
``(1) any real property belonging in whole or in part to, or leased by, the United States;
``(2) any vessel or aircraft belonging in whole or in part to, or leased by, the United States; or
``(3) any secure area of any airport,

shall be punished as provided in subsection (b) of this section.
``(b) The punishment for an offense under subsection (a) of this section is--
``(1) a fine under this title or imprisonment for not more than 5 years, or both, if the offense is committed with the intent to commit a felony; or
``(2) a fine under this title or imprisonment for not more than 6 months, or both, in any other case.

``(c) As used in this section--
``(1) the term `secure area' means an area access to which is restricted by the airport authority or a public agency; and
``(2) the term `airport' has the meaning given such term in section 47102 of title 49.''.

http://www.gpo.gov/fdsys/pkg/PLAW-10...106publ547.htm

In other words, 6 month imprisonment if you even attempt to enter a secure area with a fake document, or 5 years if you do it with intent to commit a felony. This is certainly a criminal and not a civil matter.