The Federal Trade Commission on Monday sued to prevent Microsoft and Activision-Blizzard from closing their $69 billion merger.
The filing asks the US District Court for the Northern District of California for a temporary restraining order that could keep the companies from consummating the acquisition while the FTC's in-house court is deliberating on the deal.
The FTC sued Microsoft in the agency's administrative court in December, challenging the deal as anticompetitive.
"Both a temporary restraining order and a preliminary injunction are necessary because Microsoft and Activision have represented that they may consummate the Proposed Acquisition at any time without any further notice to the Commission," the FTC's court filing said.
"We welcome the opportunity to present our case in federal court," Brad Smith, Microsoft's president, said in a statement. "We believe accelerating the legal process in the U.S. will ultimately bring more choice and competition to the market."
UK competition regulators have also challenged the deal, which promises to make Microsoft the world's third-largest video game publisher after Tencent and Sony. The acquisition would give Microsoft control over popular franchises including "Call of Duty" and "World of Warcraft."
Officials from the FTC and the UK have claimed that the deal could harm the gaming industry by allowing Microsoft to withhold Activision titles from rival platforms, such as Sony's Playstation. Microsoft has struck 10-year licensing agreements with some game platforms that will ensure those titles remain available.
Antitrust officials from the European Union blessed the deal last month, saying that Microsoft's concessions were enough to address its competition concerns.
