Microsoft has appealed the decision of the UK's Competition and Market Authority (CMA) to block its proposed acquisition of Activision Blizzard.
The CMA blocked the $69 billion acquisition in April, citing concerns about competition in the cloud gaming sector.
The EU approved the deal in May after Microsoft made concessions, and criticized the CMA's decision.
Microsoft has outlined five key grounds on which it challenges the CMA's decision in its appeal.
The CMA allegedly made fundamental errors in assessing Microsoft's position in cloud gaming services, failing to consider constraints from native gaming.
Microsoft claims the CMA failed to properly account for three long-term commercial agreements it entered into with cloud gaming providers.
The conclusion that Activision would have made its games available on cloud gaming services without the merger is considered irrational and procedurally unfair by Microsoft.
Microsoft argues that the CMA's findings of its ability and incentive to foreclose rival cloud gaming services by withholding access to Activision's gaming content after the acquisition are unlawful.
–Microsoft asserts that the CMA erred in law by imposing a comprehensive remedy, failed to consider the interests of comity, rejected the proposed Microsoft Cloud Remedy, and breached its duty of fairness and the CMA's own remedies guidance.
The appeal process is expected to be lengthy, with the UK's Competition Appeal Tribunal aiming to deal with straightforward cases within nine months.
If the appeal is successful, the acquisition will still need to go through the CMA for review.