Fans of Starbucks’ Red Cup Day might just have to wait. Starbucks workers at more than 100 U.S. stores went on strike Thursday following a tumultuous tussle with the corporation in the wake of a campaign to unionize some stores. Starbucks has vehemently opposed the unionization effort as workers have sought better pay and schedules. The corporation has faced accusations of union-busting, as well as closing some stores that successfully unionized. The strike coincided with the coffee chain’s annual Red Cup Day, where customers can get a holiday drink in a themed cup. More than 250 stores nationwide have unionized over the last year. Earlier this year, courts intervened after the company fired several union organizers in Memphis. Willow Montana, a shift manager at a store in Massachusetts, said her store voted to unionize in April, but Starbucks still hasn’t begun bargaining. “If the company won’t bargain in good faith, why should we come to work where we are understaffed, underpaid and overworked?” Montana said.