A group of 50 state attorneys general officially announced they were opening an antitrust probe into Alphabet's (GOOGL - Get Report) operations on Monday afternoon. The move had been expected for some time, and followed the announcement on Friday of a separate antitrust investigation by a group of U.S. state attorneys general into Facebook (FB - Get Report) . 

Google shares were down 0.9% to $1,194 on Monday afternoon.

The focus of the probe is on Google's advertising business, which represents more than 80% of its overall revenue; Alphabet made nearly $40 billion in its most recent quarter. 

The bipartisan effort, which is being led by the state attorney general office of Texas, was announced on Monday afternoon on the steps of the U.S. Supreme Court. California, Google's home state, and Alabama are the only two states not to join the probe. AG's from Puerto Rico and the District of Columbia are part of the probe.

On Friday, Alphabet also confirmed that the Department of Justice is investigating the company, saying that it received a civil investigative demand from the agency requesting information and documents "relating to our prior antitrust investigation." 

Last week, Google unit YouTube agreed to pay a $170 million fine for violating the online privacy of children. 

The U.S. isn't the only government probing tech giants in recent months. In July, the European Union fined Google a record $5.1 billion for abusing its power in the mobile phone market while ordering the company to alter its practices. 

Alphabet and Facebook are key holdings in Jim Cramer's Action Alerts PLUS charitable trust