The US government was suing Google Tuesday in what would be the biggest antitrust case in decades and a major test for the technology sector.

A judicial source familiar with the matter confirmed the case was being filed, after the Wall Street Journal and New York Times reported that the Justice Department suit will accuse the California tech giant of illegal monopoly behavior to preserve its dominance in internet search and advertising.

The move comes after months of investigations by federal and state antitrust enforcers seeking to check the power of the massive technology firm and parallel probes into other giants such as Amazon, Facebook and Apple.

It was not immediately clear what remedy the government was seeking in the suit, which could take years to resolve. But it could force changes in business practices or break off segments of the Google empire.

Google and other Big Tech firms have been under pressure from both the political left and right in recent years.

Progressives have claimed the massive firms have stifled competition and worsened economic inequality. A recent House of Representatives report suggested Google and others should be broken up to preserve competition. Conservatives have accused the internet giants of political bias, although evidence has been scant.

A longtime Big Tech critic, Republican Senator Josh Hawley of Missouri, said the case would be "the most important antitrust suit in a generation," and welcomed the Justice Department move.

The main unit of holding firm Alphabet, Google operates the dominant search engine used in most of the world and a variety of related services such as maps, email, advertising and shopping. It also operates the Android mobile operating system used on the majority of smartphones worldwide.

Google has been hit with big fines in the European Union for unfair competition, and has challenged those cases. The company has consistently denied claims of monopoly abuse.

News reports said 11 states, all led by Republican attorneys general, were joining the US lawsuit, suggesting a political split on the case just two weeks before the November election.

Michael Carrier, a Rutgers University law professor specializing in antitrust issues, said the case could seek to force Google to remove some of its software from Android phones, and in that sense would be similar to the Microsoft case of the 1990s where customers were forced to use proprietary programs.

But Carrier said the filing just two weeks before the election without states controlled by Democrats "raises the possibility that political concerns are playing a role here."