It's the latest action of more than three years of aggressive antitrust enforcement shepherded by FTC Chair Lina Khan, who was elevated to lead the agency by President Joe Biden after he came into office pledging tougher scrutiny of monopolistic behavior by Big Tech companies.
Khan's FTC already lost one antitrust fight with Microsoft last year when a federal judge declined to block its $69 billion takeover of video game company Activision Blizzard.
This case would go deeper into the core of Microsoft's business in a way the company hasn't experienced in the U.S. since its antitrust showdown with the Justice Department in the 1990s.
Microsoft declined to comment. Bloomberg News first reported about the investigation last week.
The case will only move forward if President-elect Donald Trump's choice to lead the FTC decides to continue the investigation and take it to court. Some analysts are expecting a lighter approach to the tech industry under Trump, though incoming Vice President JD Vance has praised Khan's work.
A number of other tech-related antitrust matters are also in play, including the Department of Justice's investigation into chipmaker Nvidia and its push to break up Google — possibly spinning off the Chrome web browser — after a federal judge ruled Google maintained an illegal monopoly for the last decade.