The union representing thousands of Starbucks workers has said it will launch its “largest strike ever” on Thursday amid the coffee chain’s annual Red Cup Day. Starbucks Workers United said in a press release on Monday that it is demanding the company bargain over staffing and scheduling issues and turn off mobile ordering on promotion days like Red Cup Day. The yearly event, during which Starbucks gives away free reusable holiday cups, is the company’s “biggest sales event of the season” and “one of the most infamously hard, understaffed days for the baristas that work them,” according to the union....