The U.S. Federal Trade Commission (FTC) is appealing a federal judge’s ruling that Microsoft could go forward with its $69 billion purchase of “Call of Duty” maker Activision Blizzard.

Microsoft’s victory in court on Tuesday, and a subsequent climbdown by Britain’s competition authority, brought the tech giant two steps closer to finalizing its tie-up with Activision, Microsoft’s biggest deal ever.

However, any outstanding regulatory hurdle makes it more likely that the agreement between Microsoft and Activision will expire on July 18 without the deal having been completed. After July 18, either company will be free to walk away from the deal unless they negotiate an extension.

The court filing had no details on the appeal, which will go before the Ninth Circuit Court of Appeals on the West Coast.

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Microsoft said it would fight the appeal.

“We’re disappointed that the FTC is continuing to pursue what has become a demonstrably weak case, and we will oppose further efforts to delay the ability to move forward,” Microsoft President Brad Smith said in an email statement.

FTC declined further comment on the notice of appeal.