Employees from the Hamilton and Hopewell township locations protested what they call unfair labor practices.
Cities including Seattle, New York City, Memphis and Los Angeles also participated in the demonstration.
Workers are demanding livable wages, consistent scheduling and safe workplaces.
In a statement, a Starbucks spokesperson said:
"Rather than publicizing rallies and protests, we encourage Workers United to live up to their obligations by responding to our proposed sessions and meeting us in-person to move the good faith bargaining process forward."