WordNet (r) 3.0 (2006):

sweatshop
    n 1: factory where workers do piecework for poor pay and are
         prevented from forming unions; common in the clothing
         industry

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "sweatshop":
   agency, atelier, barbershop, beauty parlor, beauty shop, bench,
   butcher shop, company, concern, corporation, desk, establishment,
   facility, firm, house, installation, institution, loft,
   organization, parlor, shop, studio, work site, work space,
   workbench, workhouse, working space, workplace, workroom, workshop,
   worktable