The Constitution, though, makes no mention of military involvement in
civil law enforcement one way or the other. It certainly places no restric-
tions on the use of the Army as a posse comitatus. A recent Congressional
Research Service report clearly states, “The Constitution does not explic-
itly bar the use of military forces in civilian situations or in matters of law
enforcement. . . .”
Statutory Exceptions to the Posse Comitatus Act
>10 USC 331–335: President may use the militia and armed forces to
suppress insurrection and enforce federal authority in the face of
rebellion or other forms of domestic violence.
>43 USC 1065: President may use military force to remove unlawful
enclosures from the public lands.
>22 USC 408: President may use the land and naval forces of the United
States to enforce Title IV of the Espionage Act of 1917 (22 USC 401–
408).
http://usacac.army.mil/cac2/cgsc/carl/download/csipubs/matthews.pdf