Starbucks is raising its U.S. employees’ pay and making other changes to improve working conditions in its stores. The Seattle-based coffee giant says all of its U.S. workers will earn at least $15 __ and up to $23 __ per hour by next summer. Starbucks says the enhanced pay will help it attract new workers in a tight labor environment. The company is also testing ways to streamline service and make scheduling more flexible. The actions come as workers at three Starbucks in Buffalo, New York, are attempting to form a union. Starbucks opposes that effort.