Microsoft owns the game console Xbox, while Activision Blizzard is behind major titles such as "Call of Duty" and "World of Warcraft".
Earlier in December, the Federal Trade Commission (FTC), America's counterpart to the Competition and Consumer Authority, filed a lawsuit hoping to stop the purchase.
Now, two weeks later, ten players from New Jersey, New Mexico and California have also joined together and filed another lawsuit in California federal court.
- I think there is a general uncertainty about what it will lead to, we have never seen a deal of this size, says gaming journalist Elisabeth Bergqvist.
"An aggressive advance"
The players behind the suit believe that Microsoft "risks creating a monopoly" where the company can then choose to raise the prices of its games and shut out competitors by tying titles to its own console.
However, this "console war" is something that, according to Bergqvist, has been going on for several years between the three biggest players;
Microsoft, Sony (which owns Playstation) and Nintendo.
She sees the purchase as an extension of the competition for consumers.
- Microsoft is now not only buying shares in the console sphere, but also in mobile and streaming.
It is a very aggressive advance.
Microsoft: Favoring competition
Microsoft defends the purchase and believes that it will benefit competition.
They have also offered both Sony and Nintendo access to the "Call and duty" series for the next ten years, where a new title is released annually.
Brad Smith, Microsoft's vice chairman, said in a statement that the company looks forward to presenting its case to the FTC in court.
- Even if they are now focusing on "Call of duty", we must not forget that it is about a lot of other big series, which they can lock to their platforms.
For example "World of Warcraft" or the Swedish "Candy Crush", says Elisabeth Bergqvist.