Recently acquired Proleteriat are third studio this year
Staff at another Activision Blizzard studio have formed a union.
Activision Blizzard are facing fights on other fronts.
Activision Blizzard had previously expressed their intent to fight any challenge to the deal.
Before being bought by Activision Blizzard, Proletariat were best known for developing mage royale Spellbreak.
Spellbreak is due to shut down early next year.
