The seat for Alphabet (Google) CEO Larry Page sits empty as Twitter CEO Jack Dorsey (R) and Facebook COO Sheryl Sandberg (C) testify before the Senate Intelligence Committee on Capitol Hill in Washington, DC, on September 5, 2018. Jim Watson | AFP | Getty Images

The U.S. Justice Department is preparing an investigation of Alphabet's Google to determine whether the technology company violated laws to ensure fair competition, two sources familiar with the matter said. The potential investigation, first reported on Friday, is the latest challenge for Google which already faces a raft of complaints about its business practices from rivals, as well as Democrats and Republicans. E.U. regulatory actions have already led to multibillion dollar fines and reforms to Google's business practices. The U.S. probe would focus on accusations Google gave preference to its own businesses in search results, one source said. Google declined to comment on the possible probe. The latest news underscores a growing U.S. backlash aimed at Silicon Valley companies, and marks one of the biggest steps yet by the Trump administration toward regulating a giant technology firm. The following explains the antitrust concerns about Google from other companies, critics in Washington and the EU, and how a Justice Department probe could impact the sprawling U.S. company.

Why are anti-trust regulators interested in Google?

Google's dominance of the search engine market has transformed it from a start-up into one the world's most valuable companies. Google controls much of the technology used to buy online ads, and its Android operating system runs most of the world's smartphones. Digital advertising revenue accounted for about 85% of revenue for Google's parent Alphabet last year. Some web companies, including Yelp and TripAdvisor, have long complained that Google skews search results and uses its market dominance to unfairly promote its own services over theirs. Google has said it is transparent about how it promotes its own services, and that its focus has been on benefiting consumers. The U.S. Federal Trade Commission, which enforces antitrust laws along with DOJ, previously investigated Google's business practices. The 2013 settlement with the FTC was widely viewed as a victory for Google because the company was only required to make modest changes to its practices and was allowed to continue to highlight its own services in search results. Under FTC pressure, Google agreed to end the practice of "scraping" reviews and other data from rivals' websites for its own products, and to let advertisers export data to independently assess campaigns. Europe's competition authority has taken a tougher stance against Google, handing down three fines totaling more than $9 billion in recent years. In a 2017 deal with the EU, Google agreed to pay $2.7 billion to resolve claims it unfairly steered business toward its shopping platform. In March it was fined $1.7 billion in a case focused on illegal practices in search advertising brokering from 2006 to 2016.

Could the Justice Department try to break up Google?

Sundar Pichai, CEO of Google, speaks during the company's 2017 Cloud Next event in San Francisco. Bloomberg | Getty Images

Yes, in theory, but experts have said such action against a technology firm is unlikely. The Justice Department would have to file a lawsuit and convince judges that Google has undermined competition. It is rare to break up a company but not unheard of, with Standard Oil and AT&T being the two biggest examples. Perhaps the most famous case is the government's effort to break up Microsoft. The Justice Department won a preliminary victory in 2000 but was reversed on appeal. The case settled with Microsoft intact. Justice Department antitrust probes more often result in an agreement to change certain business practices.

Why is Google under so much scrutiny?