flying picket vs work-to-rule

flying picket

noun
  • A person or group of people who can be rapidly deployed to different locations in order to picket workplaces (take part in blockades or other protests) during an industrial dispute (dispute between workers and employers). 

work-to-rule

noun
  • A labor protest in which employees do only the minimum work required by the rules of a workplace, following safety or other regulations to the letter in order to cause a slowdown. 

adj
  • Of or pertaining to such a protest. 

How often have the words flying picket and work-to-rule occurred in a corpus of books? (source: Google Ngram Viewer )