Answer: Picketing
Explanation:
Picketing is the term used to describe the actions of the union members in the question because it involves gathering outside the venue of an area with which protesters have an issue with and drawing attention to the reason for the congregation as well as discouraging people from entering the venue.
This strategy is used by union members quite a lot when they want to register displeasure with an employer. It is also used by groups that want to limit the attendance of certain events as well.
