lower-class, low-class

from The Collaborative International Dictionary of English v.0.48

blue-collar \blue-collar\ adj.
   1. of or designating work or workers in industry not
      requiring well-groomed appearance. [Narrower terms:
      {industrial}] {white-collar}
      [WordNet 1.5]

   2. of those who work for wages especially manual or
      industrial laborers. [Narrower terms: {lower-class,
      low-class}]

   Syn: propertyless, wage-earning, working-class.
        [WordNet 1.5]