Google and Microsoft are long-standing rivals. Microsoft, of course, has played the role of the old, stodgy tech stalwart, while Google has played the role of the innovative, quirky upstart.

But Google and Microsoft may soon have a lot more common. That’s because the Federal Trade Commission, spurred on in part by complaints from Google’s own advertisers, is reportedly opening a wide antitrust probe that will determine if the search giant is abusing its search dominance in an illegal manner.

According to the Wall Street Journal, “The [FTC’s] five-member panel of commissioners is preparing to send its formal demands for information to Google within days, these people said. They said other companies are likely to receive official requests for information about their dealings with Google at a later stage.

This, obviously, is bad news for Google. Even if the company is eventually cleared, the investigation that is coming looks to be the broadest and deepest the company has ever faced in the United States.

That means Google’s businesses and practices will be under the microscope for an extended period of time — perhaps more than a year.

Given the fact that Google has already been subject to informal questioning by the FTC, a formal investigation would hint that the FTC has seen enough to convince its commissioners that the search giant may have acted in an anticompetitive fashion.

Of course, none of this should really come as a surprise to Google. Antitrust talk has existed in the EU for some time, and management had to have known that it’s increasing presence in verticals dominated by some of its largest advertisers would lead to antitrust cries.

Indeed, Google’s vertical expansion has already proven problematic, and the company has essentially admitted that it promotes its own properties prominently in the SERPs.

Ironically, despite Google’s apparent desire to go beyond search in its effort to organize the world’s information, the vast majority of its revenue still comes from advertising. Vertical initiatives like Boutiques.com? Bleh.

Even more ironic: Google, like so many companies, has tried to play the game of encouraging regulators to look at antitrust-related issues related to its competition, Microsoft included.

Now that the shoe is on the other foot, we’ll see how Google walks the same path Microsoft had to.