WordNet (r) 3.0 (2006):

walkout
    n 1: a strike in which the workers walk out
    2: the act of walking out (of a meeting or organization) as a
       sign of protest; "there was a walkout by the Black members as
       the chairman rose to speak"

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "walkout":
   abandonment, apostasy, arrest, bell, betrayal, bolt, boycott,
   boycottage, breakaway, check, checkmate, cutoff, dead stop,
   deadlock, decampment, defection, departure, dereliction, deserter,
   desertion, egress, end, endgame, ending, escape, evacuation, exit,
   exodus, final whistle, flight, full stop, getaway, going,
   grinding halt, gun, halt, hegira, job action, leaving, lockout,
   outlaw strike, parting, passing, ratting, removal, retirement,
   retreat, revolt, rulebook slowdown, schism, secession, sick-in,
   sit-down, sit-down strike, slowdown, stalemate, stand, standoff,
   standstill, stay, stop, stoppage, strike, sympathy strike, tie-up,
   turnout, wildcat strike, withdrawal, work stoppage