Starbucks says it will accelerate its store closings in the U.S. next year as it tries to boost sluggish sales.

The Seattle-based company announced Tuesday it will close 150 underperforming stores in heavily penetrated markets, up from the usual rate of 50 closings a year. A list of the 150 stores was not initially released.

The company also said it expects 1 percent growth in global sales for the third quarter, a period that encompassed an uproar over the arrest of two black men at a Philadelphia Starbucks. Starbucks closed its U.S. stores May 29 to conduct racial-bias training for its employees. CEO Kevin Johnson told investors the company halted its marketing campaign for cold beverages while it addressed the controversy, which may have affected sales.

Starbucks shares slipped nearly 2 percent in after-hours trading.