These are contract workers, not Google employees. Google doesn't care whether you are unionized or not, they no doubt pick the cheapest contractor they possibly can.
Eighty Google contract workers in Pittsburgh employed by HCL America voted Tuesday to unionize with the United Steel Workers (USW). They will organize under the name Pittsburgh Association of Tech Professionals (PATP). The vote to unionize passed, with 49 voting in favor of unionization and 24 voting against unionization.