Regulators in the United Kingdom on Thursday announced an anti-trust investigation into Microsoft's $69 billion deal to purchase Activision Blizzard after the software giant declined to allay competition concerns.

The U.K.'s Competition and Markets Authority called for a "phase 2 investigation" of the mammoth deal.

For Microsoft, which makes Xbox consoles, the all-cash deal would be a win as it would expand their assets to include games like Call of Duty and Candy Crush. CNN reported that the deal would also make Microsoft the third-largest video game developer in the world.

With the case having received scrutiny in recent weeks, Microsoft issued a statement on Sept. 1.

"We will continue to engage with regulators with a spirit of transparency and openness as they review this acquisition," the statement said.

The company has since not issued any public statements regarding the acquisition.

Meanwhile, the deal was seen as a threat to markets in console and cloud gaming, the CMA said on Sept. 1. The regulator gave the company five days to address its concerns, with Microsoft reluctant to budge.

After the deadline passed, the CMA proceeded with an in-depth probe.

The European Union has made anti-trust regulation a priority in recent weeks, increasing pressure on tech firms.

On Wednesday, tech giant Google lost its anti-trust appeal with the EU and was fined $4.12 billion.

The fate of the acquisition now hinges on the CMA's investigation. Under the regulator's procedures, the deal could be cleared, face restrictions or be denied entirely.