WordNet (r) 3.0 (2006):

walk out
    v 1: stop work in order to press demands; "The auto workers are
         striking for higher wages"; "The employees walked out when
         their demand for better benefits was not met" [syn:
         strike, walk out]
    2: leave abruptly, often in protest or anger; "The customer that
       was not served walked out"
    3: leave suddenly, often as an expression of disapproval; "She
       walked out on her husband and children"

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "walk out":
   apostatize, betray, bolt, bow out, boycott, break away,
   call a strike, call it quits, close down, close shop, defect,
   depart, desert, egress, exit, get out, go on strike, go out,
   hold out, knock off, lay off, let down, lock out, make an exit,
   march out, pass out, picket, pull out, rat, revolt, run out,
   run out on, secede, secure, sell out, shut down, shut it down,
   shut up shop, sit down, slow down, stick out, strike