The charge was one of two that Starbucks has filed against Workers United since the union began organizing late last year. More than 200 Starbucks locations have unionized since December.
Employees at the Starbucks locations on Seventh Street and Bell Road in Phoenix and 107th Avenue and Indian School Road in Avondale voted in favor of unionizing.
Laila Dalton, a shift supervisor who was working to unionize the location at Scottsdale Road and Mayo Boulevard, was fired the day before union election ballots were sent out.