The UK's Competition and Markets Authority (CMA) is looking further into the in-progress merger between Microsoft and Activision Blizzard. Earlier in the month, the CMA expressed concerns that the merger would harm Microsoft's competition by locking off franchises like Call of Duty or Overwatch to Xbox. 

"On the information currently available to it, it is or may be the case that this Merger may be expected to result in a substantial lessening of competition within a market or markets in the United Kingdom,” wrote the CMA.

Microsoft was given the option to submit proposals addressing concerns by the CMA, but opted not to. As a result, the CMA is now bringing in independent investigators to further analyze the deal. 

According to a Financial Times report, the probe is said to be extensive and involve multiple regulators as the Xbox maker prepares to file its case in Brussels in the coming weeks. One person in Brussels told the Financial Times that the deal required "an extensive investigation." 

On the same day that the CMA made its worries clear, Xbox head Phil Spencer wrote a letter arguing in favor of the merger, stating that Microsoft would take a "principled path" by having games release on the same day on Xbox and other consoles, and with feature parity. 

Thus far, Microsoft has confirmed that three of Activision Blizzard's upcoming games-Overwatch 2, Diablo IV, and Call of Duty: Modern Warfare II- will be multiplatform. 

"We will continue to enable people to play with each other across platforms and across devices," wrote Spencer. "We believe that a thorough review will show that the combination of Microsoft and Activision Blizzard will benefit the industry and players."

Even with Spencer's repeated instances about being fair, it hasn't stopped Sony from voicing dissent about the incoming acquisition. The PlayStation maker has made it clear that Call of Duty is a key source for its third-party revenue, and CEO Jim Ryan recently said that Microsoft's offer to keep the shooter franchise multiplatform was insufficient.