The filing had no details on the appeal, which will go to the Ninth Circuit Court of Appeals on the West Coast.
In her 53-page order, Corley said it was not enough for the FTC to argue that "a merger might lessen competition - the FTC must show the merger will probably substantially lessen competition."
Legal scholars questioned that standard, saying that the U.S. antitrust law required the FTC to prove the proposed deal "may" harm competition, not that it "will."
The deal is Microsoft's biggest ever, and the largest in the videogame industry's history.
To address the agency's concerns, Microsoft agreed to license "Call of Duty" to rivals, including a 10-year contract with Nintendo, contingent on the merger closing.
Persons:
Jacqueline Scott Corley, Biden, Judge Corley, Corley, Diane Bartz, Muralikumar Anantharaman, Diane Craft
Organizations:
U.S . Federal Trade Commission, Microsoft, Activision, Ninth Circuit, U.S, FTC, Nintendo, Thomson
Locations:
West Coast, San Francisco