US regulators are likely serve subpoenas to Google, as part of a formal investigation into whether the Internet major abused its dominance in web-search advertising, says a media report. The Wall Street Journal has reported the civil probe, which has the potential to reshape how companies compete on the Internet, is the most serious legal threat yet to the 12-year-old company.

The probe would not necessarily lead to any federal allegations of wrongdoing against Google, the daily said.  "Federal regulators are poised to hit Google Inc with subpoenas, launching a broad, formal investigation into whether the Internet giant has abused its dominance in Web-search advertising," the report said quoting people familiar with the matter.

Generally, a subpoena refers to a directive from a government agency seeking information. Even though in recent years, Google has faced several antitrust probes, American authorities have limited its investigations largely to reviews of the company's mergers and acquisitions.

"The new inquiry, by contrast, will examine fundamental issues relating to Google's core search-advertising business, its biggest money maker," the daily noted.