The US Justice Department (DOJ) and eight states filed an antitrust lawsuit against Alphabet Inc.’s Google over alleged illegal monopolization of the digital advertising market, according to multiple media outlets. The case would be the largest corporate breakup in four decades.

“Google abuses its monopoly power to disadvantage website publishers and advertisers who dare to use competing ad tech products in a search for higher quality, or lower cost, matches,” the DOJ wrote in the complaint.

The DOJ has joined Virginia, California, Colorado, Connecticut, New Jersey, New York, Tennessee and Rhode Island in the suit.

The lawsuit is the second against Google, having filed a separate one against the company’s alleged monopoly over internet search traffic in 2020.

The plaintiffs are asking the US District Court for the Eastern District of Virginia to order the divestiture of the Google Ad Manager suite, including its publisher ad server DFP, and its ad exchange AdX.

Google controls more than a quarter of all US digital ads, according to Bloomberg data. Digital advertising accounts for nearly 80% of Google’s revenue, and its dominance in the space has been shrinking in recent years. It accounted for 36.7% of digital advertising in 2016 but had fallen to 28.8% in 2022.