A group of employees at Activision Blizzard Inc (NASDAQ:ATVI) have voted to unionise, ahead of Microsoft's US$69bn takeover of the maker of the Call of Duty video game franchise. In Middleton, Wisconsin, workers at Raven Software's quality assurance department voted 19-3 to join the Communications Workers of America (CWA) union, according to a tally by the US National Labour Relation Board on Monday.