The report comes amid discussion from politicians and the public about whether large technology companies should be broken up. Government pushback on Alphabet in search could hit at the core one of the most highly valued publicly traded companies in the world.
Alphabet racked up $136.8 billion in revenue in 2018, with 85% of it coming from advertising. Google controls more than 70% of the search engine market, according to NetMarketShare.
Google has faced antitrust pressure in the past.
In 2013, Google said it would change some practices after it agreed to a settlement with the U.S. Federal Trade Commission. The FTC had been concerned that some of Google's business practices could stifle competition
In 2010, the company received an antitrust complaint from the European Commission regarding ranking of shopping search results and ads, which resulted in Google being fined $2.7 billion in 2017, according to Alphabet's latest annual report. In 2016, the EC complained about practices related to Google's Android operating system, leading to a $5.1 billion charge in 2018.
And in March the European Union ordered Google to pay around $1.7 billion because of advertising behavior.
Recently, Google has also come under political pressure in the U.S.
President Trump has been critical of big tech, including accusing Google of political bias in its search results. In March, Trump tweeted accusations that Google's YouTube and Twitter favored Democratic opponents over him and Republicans.
Sen. Elizabeth Warren, who announced her 2020 presidential candidacy in December, has pressed for breaking up tech companies like Google. In a widely read post published on Medium in March, Warren said she was interested in appointing regulators who would be interested in undoing what she called "anti-competitive mergers," including Google's DoubleClick, Nest and Waze.
"Current antitrust laws empower federal regulators to break up mergers that reduce competition," Warren wrote.
Google wouldn't be the first U.S. technology company to face scrutiny from the Justice Department. That agency launched a major antitrust case against Microsoft in 1998 that led to several rules the company had to follow for years.
The Justice Department had no comment. Google did not respond to repeated requests for comment.