The US government filed a blockbuster lawsuit on Tuesday accusing Google of maintaining an “illegal monopoly” in online search and advertising in the country’s biggest antitrust case in decades – opening the door to a potential breakup of the Silicon Valley titan.

The politically charged case, which could take years to play out, draws new battle lines between the US government and Big Tech with potentially major implications for the sector.

Deputy Attorney General Jeffrey Rosen said the case filed with Republican state attorneys general from 11 states takes aim at Google’s dominance of the online ecosystem.

“Google is the gateway to the internet,” Rosen told reporters.

“But it has maintained its monopoly through exclusionary practices that are harmful to competition.”

The suit said these agreements include long-term agreements requiring that Google search be pre-loaded on devices and making it impossible to delete some of its apps.

The government claims Google pays billions to maintain that position, thus reinforcing its monopoly position.

The lawsuit filed in Washington contends that Google’s actions shut out competitors, and proposes that the court consider a range of remedies.

The filing calls for the court to “enjoin Google” from anticompetitive practices and consider “structural” changes to the company – which could mean breaking it up.

Google called the lawsuit “deeply flawed”.

“People use Google because they choose to – not because they’re forced to or because they can’t find alternatives,” Google general counsel Kent Walker said in a blog post.

“This lawsuit would do nothing to help consumers. To the contrary, it would artificially prop up lower-quality search alternatives, raise phone prices, and make it harder for people to get the search services they want to use.”

The move comes after months of investigations by US federal and state antitrust enforcers seeking to check the company’s power, and parallel probes into other titans such as Amazon, Facebook and Apple.

Progressives have accused the firms of stifling competition and worsening economic inequality. A recent House of Representatives report suggested Google and others should be broken up to preserve competition.

Conservatives have accused them of political bias, although evidence has been scant.