verb (v)

• recruit for a union or organize into a union(verb.social)

  Example:
  We don't allow people to come into our plant and try to unionize the workers.
  

  Synonym:
  unionise
  

  source: wordnet30
• form or join a union(verb.social)

  Example:
  The auto workers decided to unionize.
  

  Synonym:
  organise, organize, unionise
  

  source: wordnet30