Employees of Denver’s unionized Starbucks stores went on strike Saturday to protest what they say is the coffee company’s refusal to negotiate over pay and address unfair labor practice complaints. The strike organized by Starbucks Workers United started at Starbucks’ Chicago, Seattle and Los Angeles locations Friday and expanded to include stores in Denver, Columbus and Pittsburgh on Saturday. Barista Shay Mannik joined his coworkers on the picket line outside of the chain’s University Hills store Saturday morning.