WASHINGTON, Dec 8 (AFP) - The Biden administration on Thursday moved to block Microsoft's (MSFT.O) $69 billion bid to buy "Call of Duty" maker Activision Blizzard , throwing a stumbling block in front of the tech giant's plans to rapidly expand its portfolio of popular games and catch up to bigger rivals.

Microsoft, which owns the Xbox console and game network platform, said in January 2022 that it would buy Activision for $68.7 billion in the biggest gaming industry deal in history.

Without Activision and its variety of games across mobile, consoles and PCs, Microsoft could struggle to attract users to its budding subscription service for accessing games. Drawing subscribers has become a priority for big tech companies as traditional growth sources such as ad sales become less reliable.

The U.S. software company had said it wanted the deal to help it compete with gaming leaders Tencent (0700.HK) and PlayStation owner Sony (6758.T), which has criticized the deal.

But, in its complaint, the U.S. Federal Trade Commission, which enforces antitrust law, said that Microsoft had a record of hoarding valuable gaming content.

"Microsoft has already shown that it can and will withhold content from its gaming rivals," said Holly Vedova, director of the FTC’s Bureau of Competition

. "Today, we seek to stop Microsoft from gaining control over a leading independent game studio and using it to harm competition in multiple dynamic and fast-growing gaming markets."

The agency set a hearing before an administrative law judge for August 2023.

Microsoft President Brad Smith said the company would fight the FTC. "While we believed in giving peace a chance, we have complete confidence in our case and welcome the opportunity to present our case in court," he said.

The Biden administration has taken a more aggressive approach to antitrust enforcement. The U.S. Department of Justice recently stopped a $2.2 billion merger of Penguin Random House, the world's largest book publisher, and smaller U.S. rival Simon & Schuster.

"This is more evidence of the administration's and the antitrust agencies' war against big tech," said Andre Barlow of the law firm Doyle, Barlow and Mazard PLLC. Both the Trump and Biden administrations have prioritized big tech in antitrust enforcement.

Shares in Activision closed down 1.5% at $74.76, while Microsoft slipped from earlier highs but closed about 1% higher at $247.40.

Activision, which has long dreamt of being a Disney-like entertainment conglomerate, also realized it needed more tech know-how and it could be forced to trim back its roster of games to shift resources into emerging areas such as AI.