Google is to be investigated by the Federal Trade Commission over anti-trust concerns, multiple reports say.
Unlike previous anti-trust investigations of the company, which have tended to relate to acquisitions and be limited in scope, this probe will be wide-ranging and will relate to search advertising.
The FTC is concerned that Google may be manipulating search results to give unfair prominence to its own sites, such as YouTube or Google Maps. Search accounts for by far the greatest proportion of the company's business.
Google has strenuously denied this.
The FTC may issue subpoeanas to Google as early as next week.
The news has been welcomed by Fairsearch.org, an umbrella group for companies including Expedia, Travelocity and Microsoft which have objected to Google's perceived market dominance.
"The result of Google’s anti-competitive practices is to curb innovation and investment in new technologies by other companies," it says in a statement.
"These anti-competitive practices include scraping and using other companies’ content without their permission, deceptive display of search results, manipulation of search results to favor Google’s products, and the acquisition of competitive threats to Google’s dominance."
Google is already under investigation by the European Commission over similar concerns.