pink slip vs unhire

pink slip

verb
  • To terminate the employment of. 

noun
  • Notice of termination of employment. 

  • An automobile roadworthiness inspection certificate. 

  • The title document for an automobile. 

unhire

verb
  • To fire; to terminate the employment of (somebody previously hired). 

How often have the words pink slip and unhire occurred in a corpus of books? (source: Google Ngram Viewer )