(iv) Tolling for good cause.-In the case of an alien who-
(I) has been lawfully admitted or paroled into the United States,
(II) has filed a nonfrivolous application for a change or extension of status before the date of expiration of the period of stay authorized by the Attorney General, and
(III) has not been employed without authorization in the United States before or during the pendency of such application,the calculation of the period of time specified in clause (i)(I) shall be tolled during the pendency of such application, but not to exceed 120 days.
http://travel.state.gov/visa/frvi/ineligibilities/ineligibilities_1364.html