Starbucks Workers United launched an open-ended strike in at least 40 cities Thursday on Red Cup Day, one of the chain's biggest sales days of the year.The protest, which the union says involves more than 1,000 baristas in over 65 stores, comes after Workers United voted to authorize an open-ended strike after baristas and the coffee giant failed to reach a collective bargaining agreement.The strike could hurt business during Starbucks' busy holiday season, which typically provides a sales boost and will be ...