Britain’s competition watchdog has accused Google of anti-competitive behavior in the market for buying and selling advertising on websites, following similar investigations in the US and EU.

The Competition and Markets Authority (CMA) said it had found that Google had “abused its dominant position” in online advertising, to the detriment of thousands of UK publishers and advertisers.

The CMA said that while the majority of publishers and advertisers use Google’s advertising technology services to bid for and sell advertising space, Google is preventing its rivals from offering a competitive alternative.

Regulators are focusing on Google’s role in three areas: owning two tools for buying ad space, running an advertising platform that allows publishers to manage their ad space online, and managing AdX, an ad exchange that brings together advertisers and publishers in a way that matches buyers and sellers in the stock market.

“The CMA is concerned that Google is actively using its dominance in this sector to favor its own services,” the watchdog said. “Google is putting competitors at a disadvantage and preventing them from competing on a level playing field to offer publishers and advertisers better, more competitive services that will help them grow their businesses.”

In its interim findings published on Friday, the CMA found that Google abused its dominant market position by using its own buying tools and inventory tools for publishers to bolster its own ad trading position and protect it from competition since 2015. The CMA also alleged that Google blocked rival ad inventory tools (called publisher ad servers) from effectively competing with its own product, DoubleClick for Publishers.

The CMA will consider Google’s response before making a final decision.

Regulators can impose fines of up to 10% of a company’s global turnover depending on the severity of the violations, and can also issue legally binding directions to end the violations.

In a statement, Google said the CMA’s arguments were “flawed”.

“Our ad tech tools help websites and apps fund their content and help businesses of all sizes effectively reach new customers,” said Dan Taylor, Google’s vice president of global advertising. “At the heart of this lawsuit is a misinterpretation of the ad tech sector. We disagree with the CMA’s position and will respond accordingly.”

The U.S. Department of Justice and the European Commission are also investigating Google’s ad tech activities: In June 2023, EU regulators said Google may have to sell parts of its ad tech business to address concerns, while the U.S. Department of Justice is set to accuse Google in court on Monday of monopolizing the ad tech market.

Last month, a federal court ruled that Google was illegally monopolizing the internet search market, a decision that could lead to a partial breakup of the company’s business.