This paper provides new stylized facts about the responses of the part-time employment share, the transition probability from full-time to part-time and the one from part-time to full-time jobs to a negative aggregate shock. The recessionary aggregate shock is identied within a sign-restriction VAR framework by imposing a short-run negative co-movement between unemployment and vacancies. The negative aggregate shock pushes the part-time employment share up. The latter increase is mainly due to a rise in the probability at which full-time work is transformed into part-time work without an intervening spell of unemployment. Given that such transitions mainly take place at the same firm/worker pair, these findings indicate that US firms use - in addition to the creation/destruction process - within-employment reallocation to adjust their labor input in recessionary episodes.