Alphabet Inc. (GOOGL - Get Report) shares traded sharply lower Monday as investor trimmed holdings of the Google parent following a weekend issue that caused traffic congestion across key parts of its network and a report that suggested it may face a federal antitrust probe over its search engine.

Google said the network issue, which began around mid-afternoon on Sunday, affected both its Cloud and YouTube offerings and caused severe congestion and user outages in the northeastern United States. 

"The network congestion issue in eastern USA, affecting Google Cloud, G Suite, and YouTube has been resolved for all affected users as of 4:00 pm US/Pacific," Alphabet said in a statement. "We will conduct an internal investigation of this issue and make appropriate improvements to our systems to help prevent or minimize future recurrence."

"We will provide a detailed report of this incident once we have completed our internal investigation," the statement added. "This detailed report will contain information regarding SLA credits."

Google shares were marked 6.2% lower Monday to change hands at $1,037.11 each, a move that would wipe out all of its year-to-date gain and take the stock to its lowest level since January January 4.

Google's larger market issue Monday, however, centers around multiple media reports from late Friday -- first by the Wall Street Journal --- that suggested the U.S. Department of Justice is preparing a far-reaching probe into the tech giant's sprawling business.

"Potential implications for Google could include new regulations on business practices, or
an antitrust probe leading to a breakup," said Bank of America analyst Justin Post. To break up Google (on unfair search practices or too much power to influence opinion on multiple properties?), the DOJ would likely have to file a lawsuit and convince judges that Google has undermined competition."

"It is very rare to break up a company but not unheard of, with Standard Oil and AT&T as past
examples, though the government tried to break up Microsoft and failed," he added, noting a full investigation could take as many as five years to resolve.

Last year, Google was fined a record $5 billion by European antitrust authorities following a lengthy investigation into contracts that tie makers of android-operated smartphones to the exclusive sale of its apps and was hit with a further $1.7 billion penalty in March for unfairly restricting rivals from displaying ads on its platform via third parties using its AdSense tool.

Should Google find itself in the crosshairs of a similar Justice Department probe in the United States, the Mountain View, California-based group could be susceptible to fines and restrictions in its biggest and most import market. It could also, given the escalating trade tensions between Washington and Beijing, appear on the forthcoming list of "Unreliable Entities" being prepared by the Chinese government in an effort to respond to the U.S. blacklisting of Huawei Technologies last month.

"Foreign enterprises, organizations and individuals that do not comply with market rules, violate the spirit of contract, block or cut supplies to Chinese firms with non-commercial purposes, and seriously damage the legitimate rights and interests of Chinese enterprises, will be added to the list of unreliable entities," Commerce Ministry spokesman Gao Feng said Friday.