Google is facing a massive anti-trust investigation from 48 states, the District of Columbia and Puerto Rico.
More than a dozen attorneys-general made the announcement about the investigation on the steps of the US Supreme Court Monday, citing "potential monopolistic behavior" related to Google's dominance in advertising and search.
90 percent of web searches are done with Google. Critics say the search results favor advertisers and Google subsidiaries above others.
"Very compelling analysis suggest that the overwhelming number of query responses relate to Google businesses and or advertisers that pay for that slot within those links," said Karl Racine, the attorney general of the District of Columbia.
The federal government is also pursuing an anti-trust investigation into big-tech companies. The Federal Trade Commission recently imposed fines on Google and Facebook over their handling of user data.
States have worked closely together on other matters, such as the fight to curb opioid abuse. But the sheer number participating in this kind of antitrust effort is unprecedented and gives it more weight, said Utah Attorney General Sean Reyes, a Republican.
"It's just an accumulation of public frustration, whether it's from consumers, other players in the market, regulators, lawmakers," Reyes said in an interview Monday.
States haven't seriously taken up antitrust enforcement — using laws originally crafted to combat railroad and oil barons in the 19th century — since a major antitrust case against Microsoft about two decades ago. Then, state leadership helped propel federal action.
On Tuesday, several advocacy groups applauded the state attorneys general for opening their investigation into Google's marketing power.
The consumer group Public Citizen says the time has come for tech giants like Google to be held accountable for violating US antitrust laws.
Another group, Public Knowledge, says the state-led investigations are a powerful step forward after years in which the companies' market power went largely unexamined.
The advocacy groups say the action from states might also put pressure on federal antitrust enforcers, who have already opened similar investigations.
The Open Markets Institute, which favors more competition, is also weighing in with support.