picket          
noun [ C ] uk/ˈpɪk.ɪt/ us/ˈpɪk.ɪt/
 (罢工时阻止其他工人上班的)纠察队员;纠察队
a worker or group of workers who protest outside a building to prevent other workers from going inside, especially because they have a disagreement with their employers
  There were pickets outside the factory gates. 工厂门外有一些纠察队员。 
  罢工纠察时期
an occasion on which a picket happens
  The union organized a month-long picket. 工会组织了长达一个月的罢工纠察。