The US Federal Trade Commission is reportedly preparing to launch a sweeping antitrust investigation against Google, according to the Wall Street Journal. Citing people familiar with the matter, the WSJ reports that the FTC plans to serve subpoenas in the next few days, launching what is expected to be the largest probe Google has faced in the US.

As with most antitrust inquiries, the FTC plans to determine whether Google is abusing its market dominance to hinder competition. Although the probe will undoubtedly involve the company's search engine, the FTC isn't necessarily focused on search rivalries between Google, Microsoft and Yahoo. Instead, it will focus on Google's advertising business.

The WSJ's sources believe the agency is more interested in whether Google's search engine favors its own products. For instance, if a user searches for a free online photo gallery or email service, does Google unfairly list Picasa or Gmail first? Considering the company's ever-expanding portfolio, such behavior could have far-reaching consequences.

Many companies have accused Google of anticompetitive practices, including travel services such as Expedia, as well as local listings services like Yelp. It's also worth noting that this isn't Google's first run in with the FTC. The company recently settled an inquiry over Buzz, and the two nearly butted heads over Google's AdMob acquisition.

Meanwhile, the US Department of Justice is supposedly reviewing Google's buyout of Admeld, and the DoJ recently forced Google and other tech giants to abandon a pact that would prevent them from "poaching" each other's employees. The search giant is also facing heavy friction in Europe, following numerous complaints of unfair business practices.

Google and the FTC declined to comment on the WSJ's report. The information "didn't come from us," said an FTC spokeswoman. Google has repeatedly denied any wrongdoing. "It may seem obvious, but people sometimes forget this – not every website can come out on top, or even appear on the first page," Google SVP Susan Wojcicki said in November.

"There will almost always be website owners who are unhappy about their rankings," she continued. Wojcicki also noted that Google strives to be as transparent as possible without helping people game its algorithms – something that has been a serious issue in the past. "We do everything we can to ensure that the integrity of our results isn't compromised."