US regulators have asked a judge to halt Microsoft's $69 billion (£55 billion) acquisition of Activision Blizzard, the company that publishes Call of Duty.
The largest deal in the history of the video game industry, according to the US Federal Trade Commission (FTC), could "substantially lessen competition" in the market.
The decision was made after the UK blocked the agreement because it feared it would harm competition, but the EU approved it.
In August, a trial in the US will get underway.
A preliminary injunction is required, according to a court filing from the FTC. In order to assess whether "the proposed acquisition violates US antitrust law," the regulator must first "prevent interim harm.".
Regulators around the world disagree on Microsoft's proposed acquisition of Activision, and for the transaction to close, the parties need the blessing of regulatory bodies in the US, the UK, and the EU.
The acquisition was approved by the European Commission on the grounds that there would be fair competition in the market thanks to Microsoft's offer of 10-year free licensing deals, which guarantee access to Activision's PC and console games for European players and cloud game streaming services.
However, the UK's Competition and Markets Authority (CMA) blocked the transaction in April, citing concerns that the takeover would result in less innovation and fewer gaming options.
Activision and Microsoft blasted the ruling and announced they would appeal.
The company's "darkest day" in its forty years of operation in the nation, according to Microsoft President Brad Smith, was that day.
Mr. Smith responded to the FTC's announcement by saying Microsoft welcomed the "opportunity to present our case in federal court" in an effort to convince US regulators to permit the deal to go through.
In the end, he continued, "We think hastening the legal process in the US will bring more choice and competition to the market.".
For Microsoft, which is attempting to catch up to its primary rival Sony, the acquisition of Activision—which also produces Candy Crush—is seen as crucial.
Microsoft's attempt at investment, though, might be viewed as a bet on the future of video games as the company has compared its Xbox Game Pass service to Netflix for video games.
In contrast to one-time purchases, which are currently the primary method of accessing games, Microsoft thinks that players should have subscriptions to libraries in the future.
