Starbucks is closing 16 stores around the country because of repeated safety issues, including drug use and other disruptive behaviors that threaten staff. The coffee giant is closing six stores in its hometown of Seattle, six in Los Angeles, two in Portland, Oregon and one each in Philadelphia and Washington. Starbucks said employees at those stores will be given the opportunity to transfer to other stores. The closures took on heightened significance because of an ongoing unionization effort at Starbucks' U.S. stores.Starbucks Workers United, the labor group organizing the effort, said it filed unfair labor practice charges against Starbucks on behalf of the two unionized stores that are closing in Seattle. But Starbucks insisted the closures weren't related to the unionization drive.In the letter to employees, Starbucks said it is willing to make adjustments to ensure store safety, including modifying operating hours and moving furniture — or removing it — in order to give employees a clearer view of the store. The company said it's testing alarm systems and sensors to alert employees if someone is in a restroom. The company also said restrooms at some stores might be closed if they become a safety hazard.