WordNet (r) 3.0 (2006):

strikebreaker
    n 1: someone who works (or provides workers) during a strike
         [syn: scab, strikebreaker, blackleg, rat]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "strikebreaker":
   apostate, backslider, blackleg, bolter, collaborationist,
   collaborator, convert, defector, deserter, fifth columnist, fink,
   mugwump, proselyte, quisling, rat, recidivist, recreant, renegade,
   renegado, renegate, reversionist, runagate, scab, schismatic,
   seceder, secessionist, separatist, tergiversant, tergiversator,
   traitor, turnabout, turncoat, turntail