The US Justice Department has filed a lawsuit against Google, alleging that the company unfairly used its dominance in digital advertising to harm competitors.
The lawsuit calls for the divestment of Google's Google Ad Manager, including AdX.
Google has responded by saying the lawsuit would lead to higher ad fees and hinder innovation.
This is the second federal antitrust complaint filed against Google.
The US Justice Department is taking Google to court over allegations of anticompetitive behaviour.
The lawsuit alleges that Google has "used anticompetitive, exclusionary, and unlawful means" to maintain its dominance in digital advertising.
The lawsuit calls for the divestment of Google's Google Ad Manager, including AdX.
This is the second federal antitrust complaint filed against Google, which is already subject to antitrust investigations by state attorney generals and Congress.
The Justice Department's complaint alleges a web of exclusive deals that Google has struck with companies making it harder for rivals to compete, and the use of its search engine and other platforms it owns to give Google products an unfair advantage.
Critics of Google have long claimed that the company has become too powerful and is stifling competition.
The lawsuit claims that Google now controls every link in the complex chain that drives ad prices.
The Justice department has said that Google has been able to maintain its "monopoly power" over digital advertising because it has strong brand recognition, superior technology, and the advantage of vast amounts of data gathered through its search and advertising operations.
The case will likely take years to conclude and could cost Google billions of dollars if it is found to have violated antitrust law.
Google has responded by saying that the lawsuit would slow innovation and hinder small business growth.
A Google spokesman said the company will defend itself against the allegations, calling 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 said in a post on its blog.