A group of ten gamers sued the firm over its $69 billion bid to buy "Call of Duty" maker Activision Blizzard
They argued the largest-ever acquisition in the video gaming industry would unlawfully hurt competition in the sector.
It comes around two weeks after the U.S. Federal Trade Commission filed a case to block the buyout.
The gamers who filed Tuesday's lawsuit also seek to obstruct the deal.
The complaint alleged the acquisition would give Microsoft "far-outsized market power" in the video game industry.
They also argued Microsoft could eventually "foreclose rivals, reduce consumer choice" and "raise prices."
A Microsoft representative on Tuesday defended the deal, saying in a statement.
It will "expand competition and create more opportunities for gamers and game developers."
The takeover, first announced in January, also faces antitrust scrutiny in the European Union.
