The NLRB has accused Starbucks of using "illegal tactics" to deter workers from unionizing.
Starbucks also "repeatedly" closed the Buffalo stores early "to hold anti-union meetings," which reduced staff's earnings, the NLRB wrote.
Workers United – the union that the Starbucks stores are organizing with – previously said Starbucks' actions were affecting staff's stance on unionizing.
Starbucks workers in Buffalo first announced plans to unionize last August, citing understaffing, product shortages, and their experiences working during the pandemic.
In May, the NLRB also petitioned for injunctive relief for seven former Starbucks employees in Memphis, Tennessee it said were "unlawfully fired" for organizing.