Microsoft Corp. formally filed its appeal against the UK antitrust watchdog’s decision to block its $69 billion Activision Blizzard Inc. deal.

Microsoft lodged the suit at the Competition Appeal Tribunal on Wednesday, according to a company spokesperson. The anticipated move comes on the deadline to file an appeal.

The EU earlier this month waved one of the biggest deals in history through, diverging from the UK’s shock decision to block. The Competition and Markets Authority said it was standing by its decision to halt the deal, arguing that it would enable Microsoft to set the terms of the gaming market for a decade.

The judicial review process will begin and could take as long as nine months. CAT cases are usually heard by three judges including a member who has specialist knowledge.

The Microsoft spokesperson didn’t comment beyond confirming the filing. An Activision spokesperson didn’t immediately respond to a request for comment.

Meanwhile, the tech giant is yet to face the US Federal Trade Commission on the deal after it sued to block it. The trial isn’t set to begin until early August and isn’t likely to produce a decision until the end of the year.

It’s set to be a tough fight for Microsoft as the tribunal’s powers are limited to looking at the legality of the decision making process rather than the facts that it turned on. If the CAT decides there has been an error in judgment, it then sends the case back to the CMA itself. The CMA has never overturned a decision on any case that has been sent back to it from the CAT.

The CMA blocked the tie-up after its analysis found the it would solidify Microsoft’s advantage in the market by giving it control over the globally successful Call of Duty, Overwatch, and World of Warcraft titles. The watchdog found that without the merger Activision would be able to start providing games on different cloud platforms in the future.

(Updates with detail in the sixth and final paragraph)