EU antitrust regulators on Tuesday opened a full-scale investigation into Microsoft's $69 billion bid for "Call of Duty" maker Activision Blizzard, warning the deal may hurt competition.

The U.S. software company, which announced the deal in January, is betting Activision's stable of games will help it compete better with leaders Tencent and Sony, with the latter being a critic of the deal.

"The Commission's preliminary investigation shows that the transaction may significantly reduce competition on the markets for the distribution of console and PC video games, including multigame subscription services and/or cloud game streaming services, and for PC operating systems," the European Commission said in a statement.

"In particular, the Commission is concerned that, by acquiring Activision Blizzard, Microsoft may foreclose access to Activision Blizzard's console and PC video games, especially to high-profile and highly successful games (so-called ‘AAA' games) such as ‘Call of Duty'," it said.