An Amazon worker at the Bessemer, Alabama, warehouse testified last week he saw Amazon security guards use keys to open a U.S. Post Office box that was used to collect ballots on the historic union vote. The mailbox was unlawfully installed by the USPS at Amazon’s request. The labor union that organized the workers in Bessemer has accused Amazon of anti-union threats, firing an employee for distributing union cards, and creating an “impression of surveillance” during the voting period. The National Labor Relations Board continues its hearing on the case this week.