What happened

Shares of Google parent Alphabet (GOOG -1.55%) (GOOGL -1.58%) were down 6.3% as of 11 a.m. EDT Monday after The Wall Street Journal reported that the U.S. Department of Justice is preparing to launch an antitrust investigation of the tech giant.

Citing people familiar with the matter, The Journal says the Justice Department's "antitrust division in recent weeks has been laying the groundwork for the probe," spurring concerns among Alphabet investors that potential fines and/or increased regulatory oversight could follow.

Detective looking at camera through magnifying glass.

Image source: Getty Images.

So what

That's not to say the investigation guarantees a starkly negative outcome for Alphabet. Recall that the Federal Trade Commission (FTC), which shares antitrust authority with the Justice Department, previously ended its own broad investigation of Google in early 2013 without taking any specific action -- but only after the internet search giant agreed to change some business practices to ease the FTC's concerns over potentially anti-competitive behavior.

Now what

But it's also unsurprising to see shares slumping today considering Alphabet has already incurred three separate multibillion-dollar fines stemming from antitrust investigations in Europe, including a $2.7 billion tab in 2017 concerning its comparison-shopping service, a roughly $5 billion penalty in 2018 over its mobile-search products, and a $1.7 billion hit earlier this year for alleged offenses by Google's AdSense for Search business.

In each case, it's worth noting Google not only voiced its disagreement and pledged to appeal the decisions, but also easily absorbed the fines as operating expenses in their respective quarters while still generating billions in net income. Given growing scrutiny over Alphabet's ever-increasing industry dominance, however, the market is rightly irked by uncertainties surrounding this new investigation.